Display device and electronic device

ABSTRACT

A display device includes an anti-reflection film having a plurality of projections over a display screen surface. An angle made by a base and a slope of each of the plurality of projections is equal to or greater than 84° and less than 90°.

TECHNICAL FIELD

The present invention relates to a display device having ananti-reflection function.

BACKGROUND ART

In some display devices having various displays (such as a liquidcrystal display, an electroluminescent display (hereinafter alsoreferred to as an EL display), or a plasma display), there may be a casewhere it becomes difficult to see a display screen due to reflection ofits surroundings by surface reflection of external light, so thatvisibility is decreased. This is a considerable problem particularly inan increase in size of the display device and outdoor use thereof.

In order to prevent such reflection of external light, a method ofproviding a display screen of a display device with an anti-reflectionfilm has been employed. For example, there is a method of providing ananti-reflective film that has a multilayer structure of stacked layershaving different refractive indices so as to be widely effective for avisible light wavelength range (see, for example, Reference 1: JapanesePublished Patent Application No. 2003-248102). With a multilayerstructure, external light beams reflected at each interface between thestacked layers interfere and cancel each other, which provides ananti-reflection effect.

DISCLOSURE OF INVENTION

However, with the above-described multilayer structure, a light beam,which cannot be cancelled, of the external light beams reflected at eachlayer interface is emitted to a viewer side as reflected light. In orderto achieve mutual cancellation of external light beams, it is necessaryto precisely control optical characteristics of materials, thicknesses,and the like of films stacked, and it has been difficult to performanti-reflection treatment to all external light beams which are incidentfrom various angles.

In view of the foregoing, a conventional anti-reflection film has afunctional limitation, and an anti-reflection film having a higheranti-reflection function, and a display device having such ananti-reflection function have been demanded.

It is an object of the present invention to provide a high-visibilitydisplay device with an anti-reflection function that can further reducereflection of external light, and a method for manufacturing such adisplay device.

A feature of the present invention is to use an anti-reflection filmhaving a plurality of projections over a display screen surface of adisplay device as an anti-reflection film having an anti-reflectionfunction to prevent reflection of external light. Each projection of ananti-reflection film of the present invention preferably has a conicalshape, and an angle made by a base and a lateral surface of eachprojection is preferably equal to or greater than 84° and less than 90°.Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a rounded top,or the like.

In the anti-reflection film of the present invention, a ratio of a basediameter to a height of each projection is 1:5 to 1:29, preferably 1:10,and the height is preferably 1 μm to 3 μm. When each projection is ofthis size, light transmittance is not decreased, and processing isrelatively easy.

The present invention can also be applied to a display device that is adevice having a display function. The display device of the presentinvention includes, in its category, a light emitting display device inwhich a TFT is connected to a light emitting element having, betweenelectrodes, a layer containing an organic material, an inorganicmaterial, or a mixture of an organic material and an inorganic materialthat exhibits light emission called electroluminescence (hereinafteralso referred to as EL); a liquid crystal display device which uses aliquid crystal element having a liquid crystal material as a displayelement; and the like. In the present invention, the display devicerefers to a device including a display element (such as a liquid crystalelement or a light emitting element). Note that the display device mayrefer to a main body of a display panel in which a plurality of pixelseach including a display element such as a liquid crystal element or anEL element and a peripheral driver circuit for driving these pixels areformed over a substrate. In addition, the display device may include onewhich is provided with a flexible printed circuit (FPC) or a printedwiring board (PWB) (such as an IC, a resistor, a capacitor, an inductor,or a transistor). Further, the display device may include an opticalsheet such as a polarizing plate or a retardation plate. Furthermore,the display device may include a backlight (which may include a lightguiding plate, a prism sheet, a diffuser sheet, a reflective sheet, or alight source (such as an LED or a cold cathode tube)).

Note that the display element and the display device can be in variousmodes and can include various elements. For example, a display medium ofwhich contrast varies by an electromagnetic action can be used, such asan EL element (an organic EL element, an inorganic EL element, or an ELelement containing an organic material and an inorganic material), anelectron emitting element, a liquid crystal element, electronic ink, agrating light valve (GLV), a plasma display panel (PDP), a digitalmicromirror device (DMD), a piezoelectric ceramic display, or a carbonnanotube. Note that examples of display devices using the above displayelements are as follows: an EL display, as a display device using an ELelement; a field emission display (FED) or an SED flat-panel display(SED: Surface-conduction Electron-emitter Display), as a display deviceusing an electron emitting element; a liquid crystal display, atransmissive liquid crystal display, a semi-transmissive liquid crystaldisplay, or a reflective liquid crystal display, as a display deviceusing a liquid crystal element; and electronic paper, as a displaydevice using electronic ink.

One mode of the display device of the present invention includes ananti-reflection film having a plurality of projections over a displayscreen, in which an angle made by a base and a slope of each projectionis equal to or greater than 84° and less than 90°.

Another mode of the display device of the present invention includes apair of substrates, at least one of which is a light-transmittingsubstrate, a display element provided between the pair of substrates,and an anti-reflection film having a plurality of projections on anouter side of the light-transmitting substrate, in which an angle madeby a base and a slope of each projection is equal to or greater than 84°and less than 90°.

Another mode of the display device of the present invention includes apair of light-transmitting substrates, a display element providedbetween the pair of light-transmitting substrates, and a pair ofanti-reflection films each having a plurality of projections onrespective outer sides of the pair of light-transmitting substrates, inwhich an angle made by a base and a slope of each projection is equal toor greater than 84° and less than 90°.

Each projection may have a conical shape, a needle-like shape, a shapeof a cone with its apex cut off by a plane parallel to its base (atruncated conical shape), a dome shape with a rounded top, or the like.The anti-reflection film can be formed of not a material with a uniformrefractive index but a material of which a refractive index changes froma surface to a display screen side. For example, in each of theplurality of projections, a portion closer to the surface is formed of amaterial having a refractive index equivalent to air to further reducereflection, by the projection surface, of external light which isincident on each projection through air. On the other hand, a portioncloser to the substrate on the display screen side is formed of amaterial having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate.

When a glass substrate is used as the substrate, since the refractiveindex of air is smaller than that of a glass substrate, each projectionmay have such a structure in which a portion closer to a surface (anapical portion in a case of a cone) is formed of a material having alower refractive index, and a portion closer to a base of eachprojection is formed of a material having a higher refractive index, sothat the refractive index increases from the apical portion to the baseof the cone. When glass is used for the substrate, each projection canbe formed of a film including fluoride, oxide, or nitride.

The display device including the anti-reflective film of the presentinvention includes a plurality of projections on its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections. Note that an interface of a projection meansthe interface between the projection and an air in this specification.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving an anti-reflection function that can further reduce reflection ofexternal light by providing the anti-reflection film having a pluralityof projections on its surface. Accordingly, a more high-quality andhigh-performance display device can be manufactured.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C are conceptual diagrams of the present invention.

FIGS. 2A to 2C are conceptual diagrams of the present invention.

FIGS. 3A1 to 3C2 are conceptual diagrams of the present invention.

FIG. 4 is a cross-sectional view showing a display device of the presentinvention.

FIG. 5A is a top view and FIGS. 5B and 5C are cross-sectional viewsshowing a display device of the present invention.

FIGS. 6A and 6B are cross-sectional views showing a display device ofthe present invention.

FIGS. 7A and 7B are cross-sectional views showing a display device ofthe present invention.

FIGS. 8A and 8B are a top view and a cross-sectional view showing adisplay device of the present invention, respectively.

FIGS. 9A and 9B are a top view and a cross-sectional view showing adisplay device of the present invention, respectively.

FIG. 10 is a cross-sectional view showing a display device of thepresent invention.

FIG. 11 is a cross-sectional view showing a display device of thepresent invention.

FIG. 12 is a cross-sectional view showing a display device of thepresent invention.

FIG. 13 is a cross-sectional view showing a display device of thepresent invention.

FIGS. 14A and 14B are cross-sectional views each showing a displaymodule of the present invention.

FIG. 15 is a cross-sectional view showing a display module of thepresent invention.

FIGS. 16A to 16D are backlights which can be used in a display device ofthe present invention.

FIGS. 17A to 17C are top views each showing a display device of thepresent invention.

FIGS. 18A and 18B are top views each showing a display device of thepresent invention.

FIG. 19 is a block diagram showing main components of an electronicdevice to which the present invention is applied.

FIGS. 20A and 20B are diagrams each showing an electronic device of thepresent invention.

FIGS. 21A to 21E are diagrams each showing an electronic device of thepresent invention.

FIGS. 22A to 22D are cross-sectional views each showing a structure of alight emitting element applicable to the present invention.

FIGS. 23A to 23C are cross-sectional views each showing a structure of alight emitting element applicable to the present invention.

FIGS. 24A to 24C are cross-sectional views each showing a structure of alight emitting element applicable to the present invention.

FIG. 25 is a conceptual diagram of the present invention.

FIG. 26 is a diagram showing an experimental model of a comparativeexample.

FIG. 27 is a diagram showing experimental data of a comparative example.

FIG. 28 is a diagram showing an experimental model of Embodiment 1.

FIG. 29 is a diagram showing experimental data of Embodiment 1.

FIG. 30 is a diagram showing experimental data of Embodiment 1.

FIG. 31 is a diagram showing experimental data of Embodiment 2.

FIG. 32 is a diagram showing experimental data of Embodiment 2.

FIG. 33 is a diagram showing an experimental model of Embodiment 3.

FIG. 34 is a diagram showing experimental data of Embodiment 3.

FIG. 35 is a diagram showing experimental data of Embodiment 3.

FIGS. 36A and 36B are a top view and a cross-sectional view showing adisplay device of the present invention, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiment modes and embodiments of the present inventionwill be described with reference to the accompanying drawings. However,it is easily understood by a person skilled in the art that the presentinvention can be carried out in many different modes, and the mode andthe detail of the present invention can be variously changed withoutdeparting from the spirit and the scope thereof. Therefore, the presentinvention is not interpreted as being limited to the description of thefollowing embodiment modes and embodiments. Note that the same referencenumeral may be used to denote the same portions or portions havingsimilar functions in different diagrams for explaining the structure ofthe embodiment modes with reference to drawings, and repetitiveexplanation thereof is omitted.

Embodiment Mode 1

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility.

A feature of the present invention is to use an anti-reflection filmhaving a plurality of projections over a display screen surface of adisplay device as an anti-reflection film having an anti-reflectionfunction that prevents reflection of external light. Each projection ofthe anti-reflection film of the present invention preferably has aconical shape, and an angle made by a base and a lateral surface of eachprojection is preferably equal to or greater than 84° and less than 90°.

FIG. 1A shows a top view and FIGS. 1B and 1C show cross-sectional viewsof the anti-reflection film of the present invention. In FIGS. 1A to 1C,a plurality of projections 451 are provided over a display screensurface of a display device 450. FIG. 1A is a top view of the displaydevice of this embodiment mode, and FIG. 1B is a cross-sectional view ofFIG. 1A taken along a line A-B. FIG. 1C is an enlarged view of FIG. 1B.As shown in FIGS. 1A and 1B, the projections 451 are provided adjacentto each other over a display screen.

As shown in FIG. 1C, in the anti-reflection film of the presentinvention, a ratio of a base diameter L of and a height H of eachprojection 451 is 1:5 or more (1:29 or less), preferably 1:10, and theheight H is preferably 1 μm to 3 μm. When each of the projections 451 isof this size, light transmittance is not decreased, and processing isrelatively easy.

In each projection of the present invention, an angle θ made by a baseand a slope of each projection that is a protrusion is preferably equalto or greater than 84° and less than 90° as shown in FIG. 1C. When eachprojection has the above-mentioned angle, external light repeatsreflection by and transmission through the plurality of projections.Therefore, the transmittance of external light through the projectionscan be increased, and the reflectance to a viewer side can be decreased.

Since the projections are provided over the display screen surface ofthe display device 450, the base of each projection and the displayscreen surface of the display device 450 are parallel to each other.Thus, an angle made by the slope of each projection and the displayscreen surface is also preferably equal to or greater than 84° and lessthan 90° similarly, more preferably equal to or greater than 87° andless than 90°.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape, a dome shape with a rounded top, orthe like. FIGS. 2A to 2C show examples of shape of the projection. FIG.2A shows a shape having an upper base and a lower base, not a shape witha pointed top like a cone. Therefore, a cross-section on a planeperpendicular to the lower base is trapezoidal. In a projection 461provided over a display device 460 as in FIG. 2A, a distance between thelower base and the upper base is referred to as a height H in thepresent invention.

FIG. 2B shows an example in which a projection 471 having a rounded topis provided over a display device 470. In this manner, each projectionmay have a shape with a rounded top and a curvature. In this case, theheight H of each projection corresponds to a distance between the baseand the highest point of the apical portion.

FIG. 2C shows an example in which a projection 481 having a plurality ofangles, θ1 and θ2, is provided over a display device 480. In thismanner, the projection may have a shape of a stack of a cylindricalshape and a conical shape. In this case, angles made by lateral surfacesand bases are different as indicated by θ1 and θ2. In the case of theprojection 481 in FIG. 2C, θ1 is preferably equal to or greater than 84°and less than 90°, and the height H of the projection corresponds to theheight of the conical shape with an oblique lateral surface.

FIGS. 3A1 to 3C2 show examples of shape of the anti-reflection filmhaving a plurality of projections. FIGS. 3A, 3B, and 3C separately showexamples in which the plurality of projections are differently providedover a display screen surface. FIGS. 3A2, 3B2, and 3C2 are top views.FIG. 3A 1 is a cross-sectional view of FIG. 3A 2 along a line X1-Y1;FIG. 3B 1 is a cross-sectional view of FIG. 3B 2 along a line X2-Y2; andFIG. 3C 1 is a cross-sectional view of FIG. 3C 2 along a line X3-Y3.

FIGS. 3A1 and 3A2 show an example in which a plurality of projections466 a to 466 d are adjacent to each other at regular intervals over adisplay screen of a display device 465. In this manner, projections donot necessarily need to be in contact with each other over a displayscreen. In the present invention, projections provided with intervals asdescribed above are also called an anti-reflection film as a genericterm for a portion having an anti-reflection function. Thus, even whenprojections are physically discontinuous and are not in a film shape,they are referred to as an anti-reflection film.

FIGS. 3B1 and 3B2 show an example in which a plurality of projections476 a to 476 d are closely adjacent to and in contact with each otherover a display screen of a display device 475. As shown in FIGS. 3B1 and3B2, the plurality of projections are provided in contact with eachother so as to cover the display screen. When a display screen surfaceis covered with conical projections as much as possible in the abovemanner, there is an effect of an increase in the amount of light whichis incident on the anti-reflection film.

FIGS. 3C1 and 3C2 show an example in which an anti-reflection film 486having a plurality of projections is provided over a display screen of adisplay device 485. As shown in FIGS. 3C1 and 3C2, the plurality ofprojections of the anti-reflection film may be a single continuous film,and the plurality of projections may be provided on a surface of theanti-reflection film. In this manner, the anti-reflection film of thepresent invention can have various shapes each having a plurality ofprojections.

The anti-reflection film can be formed of not a material with a uniformrefractive index but a material of which a refractive index changes froma surface to a display screen side. For example, in each of theplurality of projections, a portion closer to the surface is formed of amaterial having a refractive index equivalent to air to further reducereflection, by the projection surface, of external light which isincident on each projection through air. On the other hand, a portioncloser to the substrate on the display screen side is formed of amaterial having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate. When a glass substrate is used as thesubstrate, since the refractive index of air is smaller than that of aglass substrate, each projection may have such a structure in which aportion closer to a surface (an apical portion in a case of a cone) isformed of a material having a lower refractive index, and a portioncloser to a base of each projection is formed of a material having ahigher refractive index, so that the refractive index increases from theapical portion to the base of the cone.

A material used for forming the anti-reflection film may beappropriately selected in accordance with a material of the substrateforming a display screen surface, such as silicon, nitrogen, fluorine,oxide, nitride, or fluoride. The oxide may be silicon oxide (SiO₂),boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO), aluminumoxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide (CaO),diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide (SrO),antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide (ITO), zincoxide (ZnO), indium zinc oxide (IZO) in which indium oxide is mixed withzinc oxide (ZnO), a conductive material in which indium oxide is mixedwith silicon oxide (SiO₂), organic indium, organic tin, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, or the like. The nitride may be aluminum nitride (AlN),silicon nitride (SiN), or the like. The fluoride may be lithium fluoride(LiF), sodium fluoride (NaF), magnesium fluoride (MgF₂), calciumfluoride (CaF₂), lanthanum fluoride (LaF₃), or the like. Theanti-reflection film may include one or more kinds of theabove-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.

The anti-reflection film having a plurality of projections can be formedby forming a thin film by a sputtering method, a vacuum evaporationmethod, a PVD (Physical Vapor Deposition) method, or a CVD (ChemicalVapor Deposition) method such as a low-pressure CVD (LPCVD) method or aplasma CVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, or the like can beemployed. Still alternatively, an imprinting technique or ananoimprinting technique with which a nanoscale three-dimensionalstructure can be formed by a transfer technology can be employed.Imprinting and nanoimprinting are techniques with which a minutethree-dimensional structure can be formed without using aphotolithography process.

An anti-reflection function of the anti-reflection film having aplurality of projections of the present invention is described withreference to FIG. 25. FIG. 25 shows an anti-reflection film havingadjacent projections 411 a, 411 b, 411 c, and 411 d over a displayscreen of a display device 410. External light 412 a is incident on theprojection 411 c. A part of the external light 412 a is transmitted astransmitted light 413 a, and the other part is reflected by an interfaceof the projection 411 c as reflected light 412 b. The reflected light412 b is then incident on the adjacent projection 411 b. A part of thereflected light 412 b is transmitted as transmitted light 413 b, and theother part is reflected by an interface of the projection 411 b asreflected light 412 c. The reflected light 412 c is incident again onthe adjacent projection 411 c. A part of the reflected light 412 c istransmitted as transmitted light 413 c, and the other part is reflectedby the interface of the projection 411 c as reflected light 412 d. Thereflected light 412 d is also incident again on the adjacent projection411 b, and a part of the reflected light 412 d is transmitted astransmitted light 413 d.

In this manner, the display device including the anti-reflection film ofthe present invention includes a plurality of projections on itssurface. External light is reflected to not a viewer side but anotheradjacent projection because the interface of each projection is notflat. Alternatively, external light propagates between the projections.Incident external light is partly transmitted through each projection,and reflected light is then incident on an adjacent projection. In thismanner, external light reflected by interfaces of adjacent projectionsrepeats incidence between the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

Embodiment Mode 2

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Specifically,this embodiment mode describes a case of a display device having apassive-matrix structure.

The display device includes a first electrode layer 751 a, a firstelectrode layer 751 b, and a first electrode layer 751 c which extend ina first direction; an electroluminescent layer 752 which is provided tocover the first electrode layer 751 a, the first electrode layer 751 b,and the first electrode layer 751 c; and a second electrode layer 753 a,a second electrode layer 753 b, and a second electrode layer 753 c whichextend in a second direction perpendicular to the first direction (seeFIGS. 5A and 5B). The electroluminescent layer 752 is provided betweenthe first electrode layer 751 a, the first electrode layer 751 b, andthe first electrode layer 751 c and the second electrode layer 753 a,the second electrode layer 753 b, and the second electrode layer 753 c.In addition, an insulating layer 754 functioning as a protective film isprovided to cover the second electrode layer 753 a, the second electrodelayer 753 b, and the second electrode layer 753 c (see FIGS. 5A and 5B).Note that when there is concern about the influence of a transverseelectric field between each adjacent light emitting element, theelectroluminescent layer 752 provided in each light emitting element maybe separated.

FIG. 5C shows a variation on FIG. 5B, in which a first electrode layer791 a, a first electrode layer 791 b, a first electrode layer 791 c, anelectroluminescent layer 792, a second electrode layer 793 b, and aninsulating layer 794 that is a protective layer are provided. Like thefirst electrode layer 791 a, the first electrode layer 791 b, and thefirst electrode layer 791 c in FIG. 5C, the first electrode layer mayhave a tapered shape, in which a radius of curvature changescontinuously. A shape like the first electrode layer 791 a, the firstelectrode layer 791 b, and the first electrode layer 791 c can be formedby a droplet discharge method or the like. When the first electrodelayer has such a curved surface with a curvature, the coverage thereofby an insulating layer or a conductive layer stacked is favorable.

In addition, a partition (insulating layer) may be formed to cover anend portion of the first electrode layer. The partition (insulatinglayer) functions like a wall which separates between light emittingelements. Each of FIGS. 6A and 6B shows a structure in which an endportion of the first electrode layer is covered with a partition(insulating layer).

In one example of a light emitting element shown in FIG. 6A, a partition(insulating layer) 775 is formed to have a tapered shape to cover endportions of a first electrode layer 771 a, a first electrode layer 771b, and a first electrode layer 771 c. The partition (insulating layer)775 is formed over the first electrode layer 771 a, the first electrodelayer 771 b, and the first electrode layer 771 c which are provided incontact with a substrate 779, and a substrate 778 is provided with anelectroluminescent layer 772, a second electrode layer 773 b, and aninsulating layer 774 with an insulating layer 776 interposedtherebetween.

In one example of a light emitting element shown in FIG. 6B, a partition(insulating layer) 765 has a shape having a curvature, in which acurvature radius changes continuously. A first electrode layer 761 a, afirst electrode layer 761 b, a first electrode layer 761 c, anelectroluminescent layer 762, a second electrode layer 763 b, aninsulating layer 764, and a protective layer 768 are provided.

FIG. 4 shows a passive-matrix liquid crystal display device to which thepresent invention is applied. In FIG. 4, a substrate 1700 provided withfirst pixel electrode layers 1701 a, 1701 b, and 1701 c, and aninsulating layer 1712 functioning as an orientation film faces asubstrate 1710 provided with an insulating layer 1704 functioning as anorientation film, an opposite electrode layer 1705, a colored layer 1706functioning as a color filter, and a polarizing plate 1714, with aliquid crystal layer 1703 interposed therebetween.

A feature of the present invention is to use an anti-reflection filmhaving a plurality of projections over a display screen surface of adisplay device as an anti-reflection film having an anti-reflectionfunction that prevents reflection of external light. Each projection ofthe anti-reflection film of the present invention preferably has aconical shape, and an angle made by a base and a lateral surface of eachprojection is preferably equal to or greater than 84° and less than 90°.In this embodiment mode, surfaces of the substrates 778 and 1710 andsubstrates 758, 798, and 769 on a viewer side of a display screen areprovided with anti-reflection films 777, 1707, 757, 797, and 767,respectively. Each of the anti-reflection films 777, 1707, 757, 797, and767 is an anti-reflection film having a plurality of projections, andeach projection has a conical shape in this embodiment mode.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a rounded top,or the like. The anti-reflection film can be formed of not a materialwith a uniform refractive index but a material of which a refractiveindex changes from a surface to a display screen side. For example, ineach of the plurality of projections, a portion closer to the surface isformed of a material having a refractive index equivalent to air tofurther reduce reflection, by the projection surface, of external lightwhich is incident on each projection through air. On the other hand, aportion closer to the substrate on the display screen side is formed ofa material having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate. When a glass substrate is used as thesubstrate, since the refractive index of air is smaller than that of aglass substrate, each projection may have such a structure in which aportion closer to a surface (an apical portion in a case of a cone) isformed of a material having a lower refractive index, and a portioncloser to a base of each projection is formed of a material having ahigher refractive index, so that the refractive index increases from theapical portion to the base of the cone.

A material used for forming the anti-reflection film may beappropriately selected in accordance with a material of the substrateforming a display screen surface, such as silicon, nitrogen, fluorine,oxide, nitride, or fluoride. The oxide may be silicon oxide (SiO₂),boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO), aluminumoxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide (CaO),diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide (SrO),antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide (ITO), zincoxide (ZnO), indium zinc oxide (IZO) in which indium oxide is mixed withzinc oxide (ZnO), a conductive material in which indium oxide is mixedwith silicon oxide (SiO₂), organic indium, organic tin, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, or the like. The nitride may be aluminum nitride (AlN),silicon nitride (SiN), or the like. The fluoride may be lithium fluoride(LiF), sodium fluoride (NaF), magnesium fluoride (MgF₂), calciumfluoride (CaF₂), lanthanum fluoride (LaF₃), or the like. Theanti-reflection film may include one or more kinds of theabove-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.

The anti-reflection film having a plurality of projections can be formedby forming a thin film by a sputtering method, a vacuum evaporationmethod, a PVD (Physical Vapor Deposition) method, or a CVD (ChemicalVapor Deposition) method such as a low-pressure CVD (LPCVD) method or aplasma CVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, or the like can beemployed. Still alternatively, an imprinting technique or ananoimprinting technique with which a nanoscale three-dimensionalstructure can be formed by a transfer technology can be employed.Imprinting and nanoimprinting are techniques with which a minutethree-dimensional structure can be formed without using aphotolithography process.

The display device including the anti-reflection film of the presentinvention includes a plurality of projections on its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

A glass substrate, a quartz substrate, or the like can be used as eachof the substrates 758, 769, 778, 779, 798, 1700, and 1710 and substrates759 and 799. A flexible substrate may alternatively be used. Theflexible substrate refers to a substrate which can be curved, and anexample thereof is a plastic substrate made of polycarbonate,polyarylate, polyethersulfone, or the like. Alternatively, a film (madeof polypropylene, polyester, vinyl, polyvinyl fluoride, vinyl chloride,polyamide, or the like), an inorganic film formed by evaporation, or thelike can be used.

The partition (insulating layer) 765 and the partition (insulatinglayer) 775 may be formed using an inorganic insulating material such assilicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, or aluminum oxynitride; an acrylic acid, a methacrylicacid, or a derivative thereof; a heat-resistant high molecular compoundsuch as polyimide, aromatic polyamide, or polybenzimidazole; or asiloxane resin. Alternatively, a resin material such as a vinyl resinlike polyvinyl alcohol or polyvinylbutyral, an epoxy resin, a phenolresin, a novolac resin, an acrylic resin, a melamine resin, or aurethane resin may be used. Further, an organic material such asbenzocyclobutene, parylene, fluorinated arylene ether, or polyimide, acomposition material containing a water-soluble homopolymer and awater-soluble copolymer, or the like may be used. The partition(insulating layer) 765 and the partition (insulating layer) 775 can beformed by a vapor-phase growth method such as a plasma CVD method or athermal CVD method, or a sputtering method. Alternatively, they can beformed by a droplet discharge method or a printing method (such asscreen printing or offset printing by which a pattern is formed). A filmobtained by a coating method, an SOG film, or the like can also be used.

After forming a conductive layer, an insulating layer, or the like bydischarging a composition by a droplet discharge method, a surfacethereof may be planarized by pressing with pressure to improveplanarity. As a pressing method, unevenness may be reduced by moving aroller-shaped object over the surface, or the surface may beperpendicularly pressed with a flat plate-shaped object. A heating stepmay be performed at the time of pressing. Alternatively, surfaceunevenness may be eliminated with an air knife after softening ormelting the surface with a solvent or the like. A CMP method may bealternatively used for polishing the surface. This step may be employedin planarizing the surface when unevenness is generated by a dropletdischarge method.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 3

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Thisembodiment mode describes a display device having a different structurefrom that of Embodiment Mode 2. Specifically, this embodiment modedescribes a case where the display device has an active-matrixstructure.

FIG. 36A shows a top view of the display device, and FIG. 36B shows across-sectional view of FIG. 36A taken along a line E-F. Although anelectroluminescent layer 532, a second electrode layer 533, and aninsulating layer 534 are omitted and not shown in FIG. 36A, each of themis provided as shown in FIG. 36B.

First wirings that extend in a first direction and second wirings thatextend in a second direction perpendicular to the first direction areprovided over a substrate 520 provided with an insulating layer 523 as abase film. One of the first wirings is connected to a source electrodeor a drain electrode of a transistor 521, and one of the second wiringsis connected to a gate electrode of the transistor 521. A firstelectrode layer 531 is connected to a wiring layer 525 b that is thesource electrode or the drain electrode of the transistor 521, which isnot connected to the first wiring, and a light emitting element 530 isformed using a stacked structure of the first electrode layer 531, theelectroluminescent layer 532, and the second electrode layer 533. Apartition (insulating layer) 528 is provided between adjacent lightemitting elements, and the electroluminescent layer 532 and the secondelectrode layer 533 are stacked over the first electrode layer and thepartition (insulating layer) 528. An insulating layer 534 functioning asa protective layer and a substrate 538 functioning as a sealingsubstrate are provided over the second electrode layer 533. As thetransistor 521, an inversed staggered thin film transistor is used (seeFIGS. 36A and 36B). Light which is emitted from the light emittingelement 530 is extracted from the substrate 524 side. Thus, a surface ofthe substrate 538 on a viewer side is provided with an anti-reflectionfilm 529 with a plurality of projections of the present invention.

FIGS. 36A and 36B in this embodiment mode show an example in which thetransistor 521 is a channel-etch inversed-staggered transistor. In FIGS.36A and 36B, the transistor 521 includes a gate electrode layer 502, agate insulating layer 526, a semiconductor layer 504, semiconductorlayers 503 a and 503 b having one conductivity type, wiring layers 525 aand 525 b, one of which serves as a source electrode layer and the otheras a drain electrode layer.

The semiconductor layer can be formed using the following material: anamorphous semiconductor (hereinafter also referred to as an “AS”)manufactured by a vapor-phase growth method using a semiconductormaterial gas typified by silane or germane or a sputtering method; apolycrystalline semiconductor that is formed by crystallizing theamorphous semiconductor by utilizing light energy or thermal energy; asemiamorphous (also referred to as microcrystalline or microcrystal)semiconductor (hereinafter also referred to as a “SAS”); or the like.

The SAS is a semiconductor having an intermediate structure between anamorphous structure and a crystalline structure (including a singlecrystal and a polycrystal) and having a third state which is stable interms of free energy, and includes a crystalline region havingshort-range order and lattice distortion. The SAS is formed by glowdischarge decomposition (plasma CVD) of a gas containing silicon. SiH₄is used as the gas containing silicon. Alternatively, Si₂H₆, SiH₂Cl₂,SiHCl₃, SiCl₄, SiF₄, or the like can be used. Further, F₂ or GeF₄ may bemixed. This gas containing silicon may be diluted with H₂, or H₂ and oneor more rare gas elements of He, Ar, Kr, and Ne. By further promotion oflattice distortion by inclusion of a noble gas element such as helium,argon, crypton, or neon, a favorable SAS with its stability increasedcan be obtained. The semiconductor layer may be formed by stacking anSAS layer formed from a fluorine-based gas and an SAS layer formed froma hydrogen-based gas.

The amorphous semiconductor is typified by hydrogenated amorphoussilicon, and the crystalline semiconductor is typified by polysilicon orthe like. Polysilicon (polycrystalline silicon) includes so-calledhigh-temperature polysilicon which contains polysilicon formed at aprocess temperature of 800° C. or higher as the main component,so-called low-temperature polysilicon which contains polysilicon formedat a process temperature of 600° C. or lower as the main component, andpolysilicon crystallized by adding an element which promotescrystallization or the like. Naturally, as described above, asemiamorphous semiconductor, or a semiconductor which includes acrystalline phase in a portion of a semiconductor layer can be used.

In a case where a crystalline semiconductor layer is used as thesemiconductor layer, the crystalline semiconductor layer may bemanufactured by using a laser crystallization method, a thermalcrystallization method, a thermal crystallization method using anelement which promotes crystallization such as nickel, or the like. Amicrocrystalline semiconductor, which is a SAS, can be crystallized bylaser light irradiation to improve crystallinity. In a case where theelement which promotes crystallization is not introduced, hydrogen isreleased until a concentration of hydrogen contained in an amorphoussilicon film becomes 1×10²⁰ atoms/cm³ or less by heating the amorphoussilicon layer at a temperature of 500° C. for one hour in a nitrogenatmosphere before irradiating the amorphous silicon layer with laserlight. This is because the amorphous silicon layer containing muchhydrogen is damaged when irradiated with laser light. The heat treatmentfor crystallization can be performed using a heating furnace, laserirradiation, irradiation with light emitted from a lamp (also referredto as lamp annealing), or the like. An example of a heating method is anRTA method such as a GRTA (Gas Rapid Thermal Annealing) method or anLRTA (Lamp Rapid Thermal Annealing) method. GRTA is a method forperforming heat treatment using a high-temperature gas, and LRTA is amethod for performing heat treatment by lamp light.

The crystallization may be performed by adding an element which promotescrystallization (also referred to as a catalyst element or a metalelement) to the amorphous semiconductor layer and performing heattreatment (at 550° C. to 750° C. for 3 minutes to 24 hours) in acrystallization step in which an amorphous semiconductor layer iscrystallized to form a crystalline semiconductor layer. As the elementwhich promotes crystallization, one or more elements of iron (Fe),nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au) canbe used.

Any method can be used to introduce a metal element into the amorphoussemiconductor layer as long as the method is capable of making the metalelement exist on the surface of or inside of the amorphous semiconductorlayer. For example, a sputtering method, a CVD method, a plasmatreatment method (including a plasma CVD method), an adsorption method,or a method in which a metal salt solution is applied can be employed.Among them, the method using a solution is simple and easy, andadvantageous in terms of easy concentration control of the metalelement. It is preferable to form an oxide film by irradiation with UVlight in an oxygen atmosphere, a thermal oxidation method, a treatmentwith ozone water or hydrogen peroxide including a hydroxyl radical, orthe like in order to improve wettability of the surface of the amorphoussemiconductor layer to spread an aqueous solution over the entiresurface of the amorphous semiconductor layer.

In order to remove the element which promotes crystallization from thecrystalline semiconductor layer or reduce the element, a semiconductorlayer containing an impurity element is formed in contact with thecrystalline semiconductor layer, which functions as a gettering sink.The impurity element may be an impurity element imparting n-typeconductivity, an impurity element imparting p-type conductivity, a noblegas element, or the like. For example, one or more elements ofphosphorus (P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi),boron (B), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon(Xe) can be used. A semiconductor layer containing a noble gas elementis formed in contact with the crystalline semiconductor layer containingthe element which promotes crystallization, and heat treatment (at 550°C. to 750° C. for 3 minutes to 24 hours) is performed. The element whichpromotes crystallization in the crystalline semiconductor layer movesinto the semiconductor layer containing a noble gas element; thus, theelement which promotes crystallization in the crystalline semiconductorlayer is removed or reduced. After that, the semiconductor layercontaining a noble gas element, which serves as a gettering sink, isremoved.

Laser irradiation can be performed by relatively moving a laser beam andthe semiconductor layer. In laser irradiation, a marker can also beformed in order to overlap a beam with high accuracy or control a startposition or an end position of laser irradiation. The marker may beformed over the substrate at the same time as the formation of theamorphous semiconductor film.

In a case of using laser irradiation, a continuous-wave laser beam (CWlaser beam) or a pulsed laser beam can be used. An applicable laser beamis a beam emitted from one or more kinds of the following lasers: a gaslaser such as an Ar laser, a Kr laser, or an excimer laser; a laserusing, as a medium, single-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄),YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, orGdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta isadded as a dopant; a glass laser; a ruby laser; an alexandrite laser; aTi:sapphire laser; a copper vapor laser; and a gold vapor laser. Acrystal having a large grain diameter can be obtained by irradiationwith the fundamental wave of the above laser beam or the second harmonicto the fourth harmonic of the fundamental wave thereof. For example, thesecond harmonic (532 nm) or the third harmonic (355 nm) of a Nd:YVO₄laser (the fundamental wave: 1064 nm) can be used. This laser can emiteither a CW laser beam or a pulsed laser beam. When the laser emits a CWlaser beam, a power density of the laser needs to be about 0.01 MW/cm²to 100 MW/cm² (preferably, 0.1 MW/cm² to 10 MW/cm²). A scanning rate isset to about 10 cm/sec to 2000 cm/sec for irradiation.

Note that the laser using, as a medium, single-crystalline YAG, YVO₄,forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG,Y₂O₃, YVO₄, YAlO₃, or GdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho,Er, Tm, and Ta is added as a dopant; an Ar ion laser; or a Ti:sapphirelaser can be a CW laser. Alternatively, it can be pulsed at a repetitionrate of 10 MHz or more by performing Q-switching operation, modelocking,or the like. When a laser beam is pulsed at a repetition rate of 10 MHzor more, the semiconductor layer is irradiated with a pulsed laser beamafter being melted by a preceding laser beam and before beingsolidified. Therefore, unlike a case of using a pulsed laser having alow repetition rate, the interface between the solid phase and theliquid phase can be moved continuously in the semiconductor layer, sothat crystal grains grown continuously in the scanning direction can beobtained.

When ceramic (polycrystal) is used as a medium, the medium can be formedinto a desired shape in a short time at low cost. In the case of using asingle crystal, a columnar medium having a diameter of severalmillimeters and a length of several tens of millimeters is generallyused. However, in the case of using ceramic, a larger medium can beformed.

A concentration of a dopant such as Nd or Yb in a medium, which directlycontributes to light emission, cannot be changed largely either in asingle crystal or a polycrystal. Therefore, there is limitation to someextent on improvement in laser output by increasing the concentration.However, in the case of using ceramic, the size of the medium can besignificantly increased compared with the case of using a singlecrystal, and thus, significant improvement in output can be achieved.

Furthermore, in the case of using ceramic, a medium having aparallelepiped shape or a rectangular solid shape can be easily formed.When a medium having such a shape is used and emitted light propagatesinside the medium in zigzag, an emitted light path can be extended.Therefore, the light is amplified largely and can be emitted with highoutput. In addition, since a laser beam emitted from a medium havingsuch a shape has a quadrangular shape in cross-section at the time ofemission, it has an advantage over a circular beam in being shaped intoa linear beam. By shaping the laser beam emitted as described aboveusing an optical system, a linear beam having a length of 1 mm or lesson a shorter side and a length of several millimeters to several meterson a longer side can be easily obtained. Further, by uniformlyirradiating the medium with excited light, the linear beam has a uniformenergy distribution in a long-side direction. Moreover, thesemiconductor layer is preferably irradiated with the laser beam at anincident angle θ (0°<θ<90°) because laser interference can be prevented.

By irradiating the semiconductor layer with this linear beam, the entiresurface of the semiconductor layer can be annealed more uniformly. Whenuniform annealing is needed to both ends of the linear beam, a device ofproviding slits at the both ends so as to shield a portion where energyis decayed, or the like against light is necessary.

When the linear beam with uniform intensity, which is obtained asdescribed above, is used for annealing the semiconductor layer and adisplay device is manufactured using this semiconductor layer, thedisplay device have favorable and uniform characteristics.

The laser light irradiation may be performed in an inert gas atmospheresuch as in a rare gas or nitrogen. This can suppress surface roughnessof the semiconductor layer due to laser light irradiation and variationof threshold value which is caused by variation of interface statedensity.

The amorphous semiconductor layer may be crystallized by a combinationof heat treatment and laser light irradiation, or several times of heattreatment or laser light irradiation alone.

The gate electrode layer can be formed by a sputtering method, anevaporation method, a CVD method, or the like. The gate electrode layermay be formed using an element such as tantalum (Ta), tungsten (W),titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu), chromium(Cr), or neodymium (Nd) or an alloy or compound material containing theelement as its main component. Alternatively, the gate electrode layermay be formed using a semiconductor film typified by a polycrystallinesilicon film doped with an impurity element such as phosphorus, or anAgPdCu alloy. The gate electrode layer may be a single layer or stackedlayers.

Although the gate electrode layer is formed in a tapered shape in thisembodiment mode, the present invention is not limited thereto. The gateelectrode layer may have a stacked structure, in which only one layermay have a tapered shape and the other layer may have a perpendicularside by anisotropic etching. The gate electrode layers stacked may havedifferent taper angles or the same taper angle. When the gate electrodelayer has a tapered shape, the coverage thereof with a film to bestacked thereover is improved, and defects can be reduced. Accordingly,reliability is improved.

The source electrode layer or the drain electrode layer can be formed byforming a conductive film by a PVD method, a CVD method, an evaporationmethod, or the like and then etching the conductive film into a desiredshape. Alternatively, a conductive layer can be selectively formed in adesired position by a droplet discharge method, a printing method, adispenser method, an electroplating method, or the like. Stillalternatively, a reflow method or a damascene method may be used. Thesource electrode layer or the drain electrode layer is formed using ametal such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe,Ti, Si, Ge, Zr, or Ba, or an alloy or a metal nitride thereof.Alternatively, a stacked structure thereof may be used.

The insulating layers 523, 526, 527, and 534 may be formed using aninorganic insulating material such as silicon oxide, silicon nitride,silicon oxynitride, aluminum oxide, aluminum nitride, or aluminumoxynitride; an acrylic acid, a methacrylic acid, or a derivativethereof; a heat resistant high molecular compound such as polyimide,aromatic polyamide, or polybenzimidazole; or a siloxane resin.Alternatively, a resin material such as a vinyl resin like polyvinylalcohol or polyvinylbutyral, an epoxy resin, a phenol resin, a novolacresin, an acrylic resin, a melamine resin, or a urethane resin may beused. Further, an organic material such as benzocyclobutene, parylene,fluorinated arylene ether, or polyimide, a composition materialcontaining a water-soluble homopolymer and a water-soluble copolymer, orthe like may be used. The insulating layers 523, 526, 527, and 534 canbe formed by a vapor-phase growth method such as a plasma CVD method ora thermal CVD method, or a sputtering method. Alternatively, they can beformed by a droplet discharge method or a printing method (such asscreen printing or offset printing by which a pattern is formed). A filmobtained by a coating method, an SOG film, or the like can also be used.

After forming a conductive layer, an insulating layer, or the like bydischarging a composition by a droplet discharge method, a surfacethereof may be planarized by pressing with pressure to improveplanarity. As a pressing method, unevenness may be reduced by moving aroller-shaped object over the surface, or the surface may beperpendicularly pressed with a flat plate-shaped object. A heating stepmay be performed at the time of pressing. Alternatively, surfaceunevenness may be eliminated with an air knife after softening ormelting the surface with a solvent or the like. A CMP method may bealternatively used for polishing the surface. This step may be employedin planarizing the surface when unevenness is generated by a dropletdischarge method.

Without limitation to this embodiment mode, the thin film transistor mayhave a single-gate structure in which a single channel formation regionis formed, a double-gate structure in which two channel formationregions are formed, or a triple-gate structure in which three channelformation regions are formed. In addition, a thin film transistor in aperipheral driver circuit region may also have a single-gate structure,a double-gate structure, or a triple-gate structure.

Note that without limitation to the manufacturing method of a thin filmtransistor described in this embodiment mode, the present invention canbe used in a top-gate structure (such as a staggered structure or acoplanar structure), a bottom-gate structure (such as an invertedcoplanar structure), a dual-gate structure including two gate electrodelayers provided above and below a channel region each with a gateinsulating film interposed therebetween, or other structures.

Each of FIGS. 7A and 7B shows an active-matrix liquid crystal displaydevice to which the present invention is applied. In each of FIGS. 7Aand 7B, a substrate 550 provided with a transistor 551 having amulti-gate structure, a pixel electrode layer 560, and an insulatinglayer 561 functioning as an orientation film faces a substrate 568provided with an insulating layer 563 functioning as an orientationfilm, a conductive layer 564 functioning as an opposite electrode layer,a colored layer 565 functioning as a color filter, and a polarizer (alsoreferred to as a polarizing plate) 556, with a liquid crystal layer 562interposed therebetween. A surface of the substrate 568 on a viewer sideis provided with an anti-reflection film 567 with a plurality ofprojections of the present invention.

The display device of FIG. 7A is an example in which the anti-reflectionfilm 567 is provided on an outer side of the substrate 568 and thepolarizer 556, the colored layer 565, and the conductive layer 564 aresequentially provided on an inner side. However, the polarizer 569 maybe provided on the outer side of the substrate 568 (on a viewer side) asshown in FIG. 7B, and in that case, the anti-reflection film 567 may beprovided over a surface of the polarizer 569. The stacked structure ofthe polarizer and the colored layer is also not limited to that of FIG.7A and may be appropriately determined depending on materials of thepolarizer and the colored layer or conditions of a manufacturingprocess.

FIG. 13 shows active-matrix electronic paper to which the presentinvention is applied. Although FIG. 13 shows an active-matrix type, thepresent invention can also be applied to a passive-matrix type.

Although each of FIGS. 7A and 7B shows a liquid crystal display elementas an example of a display element, a display device using a twistingball display system may be used. A twisting ball display system is amethod in which display is performed by arranging spherical particleseach of which is colored separately in black and white between the firstelectrode layer and the second electrode layer, and generating apotential difference between the first electrode layer and the secondelectrode layer so as to control the directions of the sphericalparticles.

A transistor 581 is an inverted coplanar thin film transistor, whichincludes a gate electrode layer 582, a gate insulating layer 584, wiringlayers 585 a and 585 b, and a semiconductor layer 586. In addition, thewiring layer 585 b is electrically connected to the first electrodelayers 587 a and 587 b through an opening formed in an insulating layer598. Between the first electrode layers 587 a and 587 b, and the secondelectrode layer 588, spherical particles 589, each of which includes ablack region 590 a and a white region 590 b, and a cavity 594 which isfilled with liquid around the black region 590 a and the white region590 b, are provided. A space around the spherical particle 589 is filledwith a filler 595 such as a resin (see FIG. 13). A surface of asubstrate 596 on a viewer side is provided with an anti-reflection film597 with a plurality of projections of the present invention.

Instead of the twisting ball, an electrophoretic element can also beused. A microcapsule having a diameter of approximately 10 μm to 20 μm,in which a transparent liquid, and positively charged whitemicroparticles and negatively charged black microparticles areencapsulated, is used. In the microcapsule which is provided between thefirst electrode layer and the second electrode layer, when an electricfield is applied by the first electrode layer and the second electrodelayer, the white microparticles and the black microparticles migrate toopposite sides to each other, so that white or black can be displayed. Adisplay element using this principle is an electrophoretic displayelement, and is called electronic paper in general. The electrophoreticdisplay element has higher reflectance than a liquid crystal displayelement, and thus, an auxiliary light is unnecessary, less power isconsumed, and a display portion can be recognized in a dusky place. Evenwhen power is not supplied to the display portion, an image which hasbeen displayed once can be maintained. Thus, it is possible that adisplayed image can be stored, even if a semiconductor device having adisplay function is distanced from a source of an electric wave.

The transistor may have any structure, as long as the transistor canserve as a switching element. The semiconductor layer may be formedusing various semiconductors such as an amorphous semiconductor, acrystalline semiconductor, a polycrystalline semiconductor, and amicrocrystalline semiconductor, or an organic transistor may be formedusing an organic compound.

A feature of the present invention is to use an anti-reflection filmhaving a plurality of projections over a display screen surface of adisplay device as an anti-reflection film having an anti-reflectionfunction that prevents reflection of external light. Each projection ofthe anti-reflection film of the present invention preferably has aconical shape, and an angle made by a base and a lateral surface of eachprojection is preferably equal to or greater than 84° and less than 90°.In this embodiment mode, the surfaces of the substrates 538, 568, and596 on the viewer sides of the display screens are provided with theanti-reflection films 529, 567, and 597, respectively. Each of theanti-reflection films 529, 567, and 597 is an anti-reflection filmhaving a plurality of projections, and each projection has a conicalshape in this embodiment mode.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a rounded top,or the like. The anti-reflection film can be formed of not a materialwith a uniform refractive index but a material of which a refractiveindex changes from a surface to a display screen side. For example, ineach of the plurality of projections, a portion closer to the surface isformed of a material having a refractive index equivalent to air tofurther reduce reflection, by the projection surface, of external lightwhich is incident on each projection through air. On the other hand, aportion closer to the substrate on the display screen side is formed ofa material having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate. When a glass substrate is used as thesubstrate, since the refractive index of air is smaller than that of aglass substrate, each projection may have such a structure in which aportion closer to a surface (an apical portion in a case of a cone) isformed of a material having a lower refractive index, and a portioncloser to a base of each projection is formed of a material having ahigher refractive index, so that the refractive index increases from theapical portion to the base of the cone.

A material used for forming the anti-reflection film may beappropriately selected in accordance with a material of the substrateforming a display screen surface, such as silicon, nitrogen, fluorine,oxide, nitride, or fluoride. The oxide may be silicon oxide (SiO₂),boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO), aluminumoxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide (CaO),diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide (SrO),antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide (ITO), zincoxide (ZnO), indium zinc oxide (IZO) in which indium oxide is mixed withzinc oxide (ZnO), a conductive material in which indium oxide is mixedwith silicon oxide (SiO₂), organic indium, organic tin, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, or the like. The nitride may be aluminum nitride (AlN),silicon nitride (SiN), or the like. The fluoride may be lithium fluoride(LiF), sodium fluoride (NaF), magnesium fluoride (MgF₂), calciumfluoride (CaF₂), lanthanum fluoride (LaF₃), or the like. Theanti-reflection film may include one or more kinds of theabove-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.

The anti-reflection film having a plurality of projections can be formedby forming a thin film by a sputtering method, a vacuum evaporationmethod, a PVD (Physical Vapor Deposition) method, or a CVD (ChemicalVapor Deposition) method such as a low-pressure CVD (LPCVD) method or aplasma CVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, or the like can beemployed. Still alternatively, an imprinting technique or ananoimprinting technique with which a nanoscale three-dimensionalstructure can be formed by a transfer technology can be employed.Imprinting and nanoimprinting are techniques with which a minutethree-dimensional structure can be formed without using aphotolithography process.

The display device including the anti-reflection film of the presentinvention includes a plurality of projections on its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 4

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Specifically,this embodiment mode describes a liquid crystal display device using aliquid crystal display element as a display element.

FIG. 8A is a top view of a liquid crystal display device having ananti-reflection film, and FIG. 8B is a cross-sectional view of FIG. 8Aalong a line C-D. In the top view of FIG. 8A, the anti-reflection filmis omitted.

As shown in FIG. 8A, a pixel region 606, a driver circuit region 608 athat is a scan line driver circuit, and a driver circuit region 608 bthat is a scan line driver region are sealed between a substrate 600 andan opposite substrate 695 with a sealant 692. A driver circuit region607 that is a signal line driver circuit formed using a driver IC isprovided over a substrate 600. In the pixel region 606, a transistor 622and a capacitor 623 are provided, and in the driver circuit region 608b, a driver circuit including a transistor 620 and a transistor 621 isprovided. An insulating substrate similar to that in the aboveembodiment mode can be used as the substrate 600. Although there isconcern that a substrate made of a synthetic resin generally has lowerallowable temperature limit than other substrates, the substrate can beemployed by transfer after a manufacturing process using a highheat-resistance substrate.

In the pixel region 606, the transistor 622 functioning as a switchingelement is provided over the substrate 600 with a base film 604 a and abase film 604 b interposed therebetween. In this embodiment mode, thetransistor 622 is a multi-gate thin film transistor (TFT), whichincludes a semiconductor layer including impurity regions that functionas a source region and a drain region, a gate insulating layer, a gateelectrode layer having a stacked structure of two layers, and a sourceelectrode layer and a drain electrode layer. The source electrode layeror the drain electrode layer is in contact with and electricallyconnects the impurity region of the semiconductor layer and a pixelelectrode layer 630. A thin film transistor can be manufactured by manymethods. For example, a crystalline semiconductor film is employed as anactive layer. A gate electrode is provided over a crystallinesemiconductor film with a gate insulating film interposed therebetween.An impurity element can be added to the active layer using the gateelectrode. By addition of an impurity element using the gate electrodein this manner, a mask does not need to be formed for addition of animpurity element. The gate electrode can have a single-layer structureor a stacked structure. The impurity region can be formed into ahigh-concentration impurity region and a low-concentration impurityregion by controlling the concentration thereof. A thin film transistorhaving a low-concentration impurity region in this manner is referred toas an LDD (Lightly Doped Drain) structure. The low-concentrationimpurity region can be formed to be overlapped by the gate electrode,and such a thin film transistor is referred to as a GOLD (GateOverlapped LDD) structure. The thin film transistor is formed to have ann-type polarity by using phosphorus (P) in the impurity region. In acase of a p-type polarity, boron (B) or the like may be added. Afterthat, an insulating film 611 and an insulating film 612 are formed tocover the gate electrode and the like. Dangling bonds of the crystallinesemiconductor film can be terminated by a hydrogen element mixed in theinsulating film 611 (and the insulating film 612).

In order to further improve planarity, an insulating film 615 and aninsulating film 616 may be formed as interlayer insulating films. Theinsulating film 615 and the insulating film 616 can be formed using anorganic material, an inorganic material, or a stacked structure thereof.For example, the insulating film 615 and the insulating film 616 can beformed of a material selected from substances including an inorganicinsulating material such as silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, aluminum nitride, aluminumoxynitride, aluminum nitride oxide having a higher content of nitrogenthan that of oxygen, aluminum oxide, diamond-like carbon (DLC),polysilazane, a nitrogen-containing carbon (CN), PSG (phosphosilicateglass), BPSG (borophosphosilicate glass), and alumina. Alternatively, anorganic insulating material may be used; an organic material may beeither photosensitive or non-photosensitive; and polyimide, acrylic,polyamide, polyimide amide, a resist, benzocyclobutene, a siloxaneresin, or the like can be used. Note that the siloxane resin correspondsto a resin having Si—O—Si bonds. Siloxane has a skeleton structureformed from a bond of silicon (Si) and oxygen (O). As a substituent, anorganic group containing at least hydrogen (for example, an alkyl groupor aromatic hydrocarbon) is used. A fluoro group may be used as thesubstituent. Alternatively, an organic group containing at leasthydrogen and a fluoro group may be used as the substituent.

By using a crystalline semiconductor film, the pixel region and thedriver circuit region can be formed over the same substrate. In thatcase, the transistor in the pixel region and the transistor in thedriver circuit region 608 b are formed simultaneously. The transistorused in the driver circuit region 608 b constitutes a part of a CMOScircuit. Although the thin film transistor included in the CMOS circuithas a GOLD structure, it may have an LDD structure like the transistor622.

Without limitation to this embodiment mode, the thin film transistor ofthe pixel region may have a single-gate structure in which a singlechannel formation region is formed, a double-gate structure in which twochannel formation regions are formed, or a triple-gate structure inwhich three channel formation regions are formed. In addition, the thinfilm transistor of a peripheral driver circuit region may also have asingle-gate structure, a double-gate structure, or a triple-gatestructure.

Note that without limitation to the manufacturing method of a thin filmtransistor described in this embodiment mode, the present invention canbe used in a top-gate structure (such as a staggered structure), abottom-gate structure (such as an inverted staggered structure), adual-gate structure including two gate electrode layers provided aboveand below a channel region each with a gate insulating film interposedtherebetween, or another structure.

Next, an insulating layer 631 called an orientation film is formed by aprinting method or a droplet discharge method to cover the pixelelectrode layer 630 and the insulating film 616. Note that theinsulating layer 631 can be selectively formed by using a screenprinting method or an offset printing method. After that, rubbingtreatment is performed. The rubbing treatment is not necessarilyperformed when the mode of liquid crystal is, for example, a VA mode. Aninsulating layer 633 functioning as an orientation film is similar tothe insulating layer 631. Then, the sealant 692 is formed by a dropletdischarge method in a peripheral region of the pixel region.

After that, the opposite substrate 695 provided with the insulatinglayer 633 functioning as an orientation film, a conductive layer 634functioning as an opposite electrode, a colored layer 635 functioning asa color filter, a polarizer 641 (also referred to as a polarizingplate), and an anti-reflection film 642 is attached to the substrate 600that is a TFT substrate with a spacer 637 interposed therebetween, and aliquid crystal layer 632 is provided in a gap therebetween. Since theliquid crystal display device of this embodiment mode is of transmissivetype, a polarizer (polarizing plate) 643 is provided on a side of thesubstrate 600 opposite to the side of having elements. The polarizer canbe provided over the substrate using an adhesive layer. The sealant maybe mixed with a filler, and further, the opposite substrate 695 may beprovided with a shielding film (black matrix), or the like. Note thatthe color filter or the like may be formed of materials exhibiting red(R), green (G), and blue (B) when the liquid crystal display deviceperforms full color display. When performing monochrome display, thecolored layer may be omitted or formed of a material exhibiting at leastone color.

The display device in FIGS. 8A and 8B is an example in which theanti-reflection film 642 is provided on an outer side of the oppositesubstrate 695 and the polarizer 641, the colored layer 635, and theconductive layer 634 are sequentially provided on an inner side.However, the polarizer may be provided on the outer side of thesubstrate 695 (on a viewer side), and in that case, the anti-reflectionfilm may be provided over a surface of the polarizer (polarizing plate).The stacked structure of the polarizer and the colored layer is also notlimited to FIGS. 8A and 8B and may be appropriately determined dependingon materials of the polarizer and the colored layer or conditions of amanufacturing process.

Note that the color filter is not provided in some cases wherelight-emitting diodes (LEDs) of RGB or the like are arranged as abacklight and a successive additive color mixing method (fieldsequential method) in which color display is performed by time divisionis employed. The black matrix is preferably provided so as to overlap atransistor and a CMOS circuit for the sake of reducing reflection ofexternal light by wirings of the transistor and the CMOS circuit. Notethat the black matrix may be provided so as to overlap a capacitor. Thisis because reflection by a metal film forming the capacitor can beprevented.

The liquid crystal layer can be formed by a dispenser method (droppingmethod), or an injecting method by which liquid crystal is injectedusing a capillary phenomenon after attaching the substrate 600 includingan element to the opposite substrate 695. A dropping method ispreferably employed when using a large-sized substrate to which it isdifficult to apply an injecting method.

Although the spacer may be provided in such a way that particles eachhaving a size of several micrometers are sprayed, the spacer in thisembodiment mode is formed by a method in which a resin film is formedover an entire surface of the substrate and then etched. A material ofthe spacer is applied by a spinner and then subjected to light exposureand development to form a predetermined pattern. Moreover, the materialis heated at 150° C. to 200° C. in a clean oven or the like so as to behardened. The thus manufactured spacer can have various shapes dependingon the conditions of the light exposure and development. It ispreferable that the spacer have a columnar shape with a flat top so thatmechanical strength of the liquid crystal display device can be securedwhen the opposite substrate is attached. The shape can be conical,pyramidal, or the like, and there is no particular limitation on theshape.

Subsequently, a terminal electrode layer 678 electrically connected tothe pixel portion is provided with an FPC 694 that is a wiring board forconnection, through an anisotropic conductive layer 696. The FPC 694functions to transmit external signals or potential. Through the abovesteps, a liquid crystal display device having a display function can bemanufactured.

A wiring and a gate electrode layer which are included in thetransistor, the pixel electrode layer 630, and the conductive layer 634that is an opposite electrode layer can be formed using a materialselected from indium tin oxide (ITO), indium zinc oxide (IZO) in whichindium oxide is mixed with zinc oxide (ZnO), a conductive material inwhich indium oxide is mixed with silicon oxide (SiO₂), organoindium,organotin, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide, orindium tin oxide containing titanium oxide; a metal such as tungsten(W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V),niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni),titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu) or silver (Ag),an alloy thereof, or metal nitride thereof.

The polarizing plate and the liquid crystal layer may be stacked with aretardation plate interposed therebetween.

A feature of the present invention is to use an anti-reflection filmhaving a plurality of projections over a display screen surface of adisplay device as an anti-reflection film having an anti-reflectionfunction that prevents reflection of external light. Each projection ofthe anti-reflection film of the present invention preferably has aconical shape, and an angle made by a base and a lateral surface of eachprojection is preferably equal to or greater than 84° and less than 90°.In this embodiment mode, the surface of the opposite substrate 695 on aviewer side of a display screen is provided with the anti-reflectionfilm 642. The anti-reflection film 642 is an anti-reflection film havinga plurality of projections, and each projection has a conical shape inthis embodiment mode.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a round apex, orthe like. The anti-reflection film can be formed of not a material witha uniform refractive index but a material of which a refractive indexchanges from a surface to a display screen side. For example, in each ofthe plurality of projections, a portion closer to the surface is formedof a material having a refractive index equivalent to that of air tofurther reduce reflection, by the projection surface, of external lightwhich is incident on each projection through air. On the other hand, aportion closer to the substrate side on the display screen side isformed of a material having a refractive index equivalent to that of thesubstrate to reduce reflection, by an interface between each projectionand the substrate, of external light which propagates inside eachprojection and is incident on the substrate. When a glass substrate isused as the substrate, since the refractive index of air is smaller thanthat of a glass substrate, each projection may have such a structure inwhich a portion closer to a surface (an apical portion in a case of acone) is formed of a material having a lower refractive index, and aportion closer to a base of each projection is formed of a materialhaving a higher refractive index, so that the refractive index increasesfrom the apical portion of the cone to the base of the cone.

The display device including the anti-reflection film of the presentinvention includes a plurality of projections on its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 5

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Specifically,this embodiment mode describes a light emitting display device using alight emitting element as a display element. A manufacturing method ofthe display device in this embodiment mode is described in detail withreference to FIGS. 9A and 9B and FIG. 12.

As a base film, a base film 101 a is formed using a silicon nitrideoxide film with a thickness of 10 nm to 200 nm (preferably 50 nm to 150nm) over a substrate 100 having an insulating surface, and a base film101 b is formed thereover using a silicon oxynitride film with athickness of 50 nm to 200 nm (preferably 100 nm to 150 nm), by asputtering method, a PVD (Physical Vapor Deposition) method, a CVD(Chemical Vapor Deposition) method such as a low-pressure CVD (LPCVD)method or a plasma CVD method, or the like. Alternatively, an acrylicacid, a methacrylic acid, or a derivative thereof; a heat-resistant highmolecular compound such as polyimide, aromatic polyamide, orpolybenzimidazole; or a siloxane resin may be used. Alternatively, aresin material such as a vinyl resin like polyvinyl alcohol orpolyvinylbutyral, an epoxy resin, a phenol resin, a novolac resin, anacrylic resin, a melamine resin, or a urethane resin may be used.Further, an organic material such as benzocyclobutene, parylene,fluorinated arylene ether, or polyimide, a composition materialcontaining a water-soluble homopolymer and a water-soluble copolymer, orthe like may be used. Moreover, an oxazole resin can be used, and forexample, a photo-curing polybenzoxazole or the like can be used.

A droplet discharge method, a printing method (a method for forming apattern such as screen printing or offset printing), a coating methodsuch as a spin coating method, a dipping method, a dispenser method, orthe like can also be used. In this embodiment mode, the base film 101 aand the base film 101 b are formed by a plasma CVD method. As thesubstrate 100, a glass substrate, a quartz substrate, or a siliconsubstrate, a metal substrate, or a stainless steel substrate providedwith an insulating film on the surface may be used. In addition, aplastic substrate having heat resistance sufficient to withstand aprocessing temperature of this embodiment mode may be used, or aflexible film-like substrate may be used. As the plastic substrate, asubstrate made of PET (polyethylene terephthalate), PEN(polyethylenenaphthalate), or PES (polyethersulfone) can be used, and asthe flexible substrate, a substrate made of a synthetic resin such asacrylic can be used. Since the display device manufactured in thisembodiment mode has a structure in which light from a light emittingelement is extracted through the substrate 100, the substrate 100 needsto have a light-transmitting property.

The base film can be formed using silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like and may haveeither a single-layer structure or a stacked structure of two or morelayers.

Next, a semiconductor film is formed over the base film. Thesemiconductor film may be formed with a thickness of 25 nm to 200 nm(preferably, 30 nm to 150 nm) by any of various methods (such as asputtering method, an LPCVD method, or a plasma CVD method). In thisembodiment mode, it is preferable to use a crystalline semiconductorfilm which is obtained by crystallizing an amorphous semiconductor filmwith a laser beam.

The semiconductor film obtained in this manner may be doped with aslight amount of an impurity element (boron or phosphorus) to control athreshold voltage of a thin film transistor. This doping with animpurity element may be performed to the amorphous semiconductor filmbefore the crystallization step. When the doping with an impurityelement is performed to the amorphous semiconductor film, activation ofthe impurity element can be performed by subsequent heat treatment forcrystallization. In addition, defects and the like caused by doping canbe improved.

Next, the crystalline semiconductor film is etched into a desired shapeto form a semiconductor layer.

The etching may be performed by either plasma etching (dry etching) orwet etching; however, plasma etching is suitable for treating alarge-sized substrate. As an etching gas, a fluorine-based gas such asCF₄ or NF₃ or a chlorine-based gas such as Cl₂ or BCl₃ is used, to whichan inert gas such as He or Ar may be appropriately added. Alternatively,electric discharge machining can be performed locally when the etchingis performed using atmospheric pressure discharge, in which case a masklayer does not need to be formed over the entire surface of thesubstrate.

In the present invention, a conductive layer forming a wiring layer oran electrode layer, a mask layer used for forming a predeterminedpattern, or the like may be formed by a method capable of selectivelyforming a pattern, such as a droplet discharge method. A dropletdischarge (ejection) method (also referred to as an ink-jet methoddepending on its method) can form a predetermined pattern (of aconductive layer or an insulating layer) by selectively discharging(ejecting) droplets of a composition mixed for a specific purpose. Inthis case, treatment for controlling wettability or adhesiveness may beperformed to a subject region. Alternatively, a method by which apattern can be transferred or drawn, such as a printing method (a methodfor forming a pattern such as screen printing or offset printing) or adispenser method can be used.

A mask used in this embodiment mode is formed using a resin materialsuch as an epoxy resin, an acrylic resin, a phenol resin, a novolacresin, a melamine resin, or a urethane resin. Alternatively, an organicmaterial such as benzocyclobutene, parylene, fluorinated arylene ether,or polyimide having a light-transmitting property; a compound materialmade by polymerization of a siloxane-based polymer or the like; acomposition material containing a water-soluble homopolymer and awater-soluble copolymer; or the like may be used. Still alternatively, acommercial resist material containing a photosensitizer may be used. Forexample, a positive type resist or a negative type resist may be used.In a case of using a droplet discharge method, even when using any ofthe above materials, a surface tension and a viscosity are appropriatelycontrolled by adjusting the concentration of a solvent or adding asurfactant or the like.

A gate insulating layer 107 is formed to cover the semiconductor layer.The gate insulating layer is formed using an insulating film containingsilicon with a thickness of 10 nm to 150 nm by a plasma CVD method, asputtering method, or the like. The gate insulating layer may be formedusing a known material such as an oxide material or nitride material ofsilicon typified by silicon nitride, silicon oxide, silicon oxynitride,or silicon nitride oxide, and it may have either a single-layerstructure or a stacked structure. The gate insulating layer may beformed to have a three-layer structure of a silicon nitride film, asilicon oxide film, and a silicon nitride film. Alternatively, a singlelayer of a silicon oxynitride film or a stacked layer of two layers maybe used.

Next, a gate electrode layer is formed over the gate insulating layer107. The gate electrode layer can be formed by a sputtering method, anevaporation method, a CVD method, or the like. The gate electrode layermay be formed using an element selected from tantalum (Ta), tungsten(W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper, (Cu),chromium (Cr), and neodymium (Nd), or an alloy material or a compoundmaterial containing the above element as its main component.Alternatively, the gate electrode layer may be formed using asemiconductor film typified by a polycrystalline silicon film doped withan impurity element such as phosphorus, or an AgPdCu alloy. The gateelectrode layer may be a single layer or stacked layers.

Although the gate electrode layer is formed in a tapered shape in thisembodiment mode, the present invention is not limited thereto. The gateelectrode layer may have a stacked structure in which only one layer hasa tapered shape and the other layer has a perpendicular side byanisotropic etching. The gate electrode layers stacked may havedifferent taper angles or the same taper angle, as in this embodimentmode. When the gate electrode layer has a tapered shape, the coveragethereof by a film to be stacked thereover is improved, and defects canbe reduced. Accordingly, reliability is improved.

Through the etching step in forming the gate electrode layer, the gateinsulating layer 107 may be etched to a certain extent and the thicknessthereof may be reduced (so-called film reduction).

An impurity element is added to the semiconductor layer to form animpurity region. The impurity region can be formed into ahigh-concentration impurity region and a low-concentration impurityregion by controlling the concentration thereof. A thin film transistorhaving a low-concentration impurity region is referred to as an LDD(Lightly Doped Drain) structure. The low-concentration impurity regioncan be formed to be overlapped by the gate electrode, and such a thinfilm transistor is referred to as a GOLD (Gate Overlapped LDD)structure. The thin film transistor is formed to have an n-type polarityby using phosphorus (P) in the impurity region. In a case of a p-typepolarity, boron (B) or the like may be added.

In this embodiment mode, a region where the impurity region isoverlapped by the gate electrode layer with the gate insulating layerinterposed therebetween is referred to as a Lov region, and a regionwhere the impurity region is not overlapped by the gate electrode layerwith the gate insulating layer interposed therebetween is referred to asa Loff region. In FIG. 9B, the impurity regions are indicated byhatching and white, which does not mean that an impurity element is notadded to the white portion. They are indicated in this manner so that itis easily recognized that the concentration distribution of an impurityelement in this region reflects a mask or conditions of doping. Notethat this applies to other drawings of this specification.

Heat treatment, intense light irradiation, or laser light irradiationmay be performed to activate the impurity element. At the same time asthe activation, plasma damage to the gate insulating layer and theinterface between the gate insulating layer and the semiconductor layercan be repaired.

Then, a first interlayer insulating layer is formed to cover the gateelectrode layer and the gate insulating layer. In this embodiment mode,the first interlayer insulating layer has a stacked structure of aninsulating film 167 and an insulating film 168. The insulating film 167and the insulting film 168 can be formed using a silicon nitride film, asilicon nitride oxide film, a silicon oxynitride film, a silicon oxidefilm, or the like by a sputtering method or a plasma CVD method, oranother insulating film containing silicon may be used as a single layeror a stacked structure of three or more layers.

In addition, heat treatment is performed in a nitrogen atmosphere at300° C. to 550° C. for 1 to 12 hours to hydrogenate the semiconductorlayer. Preferably, it is performed at 400° C. to 500° C. This step is astep of terminating dangling bonds of the semiconductor layer withhydrogen which is contained in the insulating film 167 that is theinterlayer insulating layer. In this embodiment mode, heat treatment isperformed at 410° C.

The insulating film 167 and the insulating film 168 can be formed usinga material selected from substances including an inorganic insulatingmaterial, such as aluminum nitride (AlN), aluminum oxynitride (AlON),aluminum nitride oxide (AlNO) having a higher content of nitrogen thanthat of oxygen, aluminum oxide, diamond-like carbon (DLC),nitrogen-containing carbon (CN), and polysilazane. Alternatively, amaterial containing siloxane may be used. An organic insulating materialmay be used, and as an organic material, polyimide, acrylic, polyamide,polyimide amide, a resist, or benzocyclobutene can be used. Moreover, anoxazole resin can be used, and for example, a photo-curingpolybenzoxazole or the like can be used.

Next, a contact hole (opening) is formed in the insulating film 167, theinsulating film 168, and the gate insulating layer 107 using a mask madeof a resist so as to reach the semiconductor layer. A conductive film isformed to cover the opening, and the conductive film is etched to form asource electrode layer or a drain electrode layer which is electricallyconnected to a part of a source region or a drain region. The sourceelectrode layer or drain electrode layer can be formed by forming aconductive film by a PVD method, a CVD method, an evaporation method, orthe like and then etching the conductive film into a desired shape. Aconductive layer can be selectively formed in a predetermined positionby a droplet discharge method, a printing method, a dispenser method, anelectroplating method, or the like. Furthermore, a reflow method or adamascene method may be used. The source electrode layer or drainelectrode layer is formed using a metal such as Ag, Au, Cu, Ni, Pt, Pd,Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Si, Ge, Zr, or Ba, or an alloy ora metal nitride thereof. In addition, it may have a stacked structurethereof.

Through the above steps, an active matrix substrate can be manufactured,which includes a thin film transistor 285 that is a p-channel thin filmtransistor having a p-type impurity region in a Lov region and a thinfilm transistor 275 that is an n-channel thin film transistor having ann-type impurity region in a Lov region in a peripheral driver circuitregion 204, and a thin film transistor 265 that is a multi-channeln-channel thin film transistor having an n-type impurity region in aLoff region and a thin film transistor 245 that is a p-channel thin filmtransistor having a p-type impurity region in a Lov region in the pixelregion 206.

Without limitation to this embodiment mode, a thin film transistor mayhave a single-gate structure in which a single channel formation regionis formed, a double-gate structure in which two channel formationregions are formed, or a triple-gate structure in which three channelformation regions are formed. In addition, the thin film transistor inthe peripheral driver circuit region may also have a single-gatestructure, a double-gate structure, or a triple-gate structure.

Next, an insulating film 181 is formed as a second interlayer insulatinglayer. In FIGS. 9A and 9B, a reference numeral 201 denotes a separationregion for separation by scribing; 202, an external terminal connectionregion which is an attachment portion of an FPC; 203, a wiring regionwhich is a lead wiring region of a peripheral portion; 204, a peripheraldriver circuit region; 205, a connection region; and 206, a pixelregion. In the wiring region 203, a wiring 179 a and a wiring 179 b areprovided, and in the external terminal connection region 202, a terminalelectrode layer 178 connected to an external terminal is provided.

The insulating film 181 can be formed of a material selected fromsubstances including an inorganic insulating material such as siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide,aluminum nitride (AlN), aluminum oxide containing nitrogen (alsoreferred to as aluminum oxynitride) (AlON), aluminum nitride containingoxygen (also referred to as aluminum nitride oxide) (AlNO), aluminumoxide, diamond-like carbon (DLC), nitrogen-containing carbon (CN), PSG(phosphosilicate glass), BPSG (borophosphosilicate glass), and alumina.Alternatively, a siloxane resin may be used. Furthermore, an organicinsulating material may be used; an organic material may be eitherphotosensitive or non-photosensitive; and polyimide, acrylic, polyamide,polyimide amide, a resist, benzocyclobutene, polysilazane, or alow-dielectric constant (Low-k) material can be used. Moreover, anoxazole resin can be used, and for example, a photo-curingpolybenzoxazole or the like can be used. Since an interlayer insulatinglayer provided for planarization needs to have high heat resistance,high insulating property, and high planarity, the insulating film 181 ispreferably formed by a coating method typified by a spin coating method.

Instead, the insulating film 181 can be formed by dipping, spraycoating, a doctor knife, a roll coater, a curtain coater, a knifecoater, CVD, evaporation, or the like. The insulating film 181 may beformed by a droplet discharge method. In a case of using a dropletdischarge method, a material liquid can be saved. Alternatively, amethod like a droplet discharge method by which a pattern can betransferred or drawn, such as a printing method (a method for forming apattern such as screen printing or offset printing), a dispenser method,or the like can be used.

A minute opening, that is, a contact hole is formed in the insulatingfilm 181 in the pixel region 206.

Next, a first electrode layer 185 (also referred to as a pixel electrodelayer) is formed in contact with the source electrode layer or the drainelectrode layer. The first electrode layer 185 functions as an anode ora cathode, and may be formed using a film containing as its maincomponent an element selected from Ti, Ni, W, Cr, Pt, Zn, Sn, In, and Moor an alloy or compound material containing the above element such asTiN, TiSi_(X)N_(Y), WSi_(X), WN_(X), WSi_(X)N_(Y), or NbN, or a stackedfilm thereof with a total thickness of 100 nm to 800 nm.

In this embodiment mode, the display device has a structure in which alight emitting element is used as a display element and light from thelight emitting element is extracted through the first electrode layer185; therefore, the first electrode layer 185 has a light transmittingproperty. The first electrode layer 185 is formed by forming atransparent conductive film and then etching the transparent conductivefilm into a desired shape.

In the present invention, the first electrode layer 185 that is alight-transmitting electrode layer may be specifically formed using atransparent conductive film made of a conductive material having a lighttransmitting property, such as indium oxide containing tungsten oxide,indium zinc oxide containing tungsten oxide, indium oxide containingtitanium oxide, or indium tin oxide containing titanium oxide. It isneedless to say that indium tin oxide (ITO), indium zinc oxide (IZO),indium tin oxide to which silicon oxide is added (ITSO), or the like canalso be used.

Even in a case of using a material such as a metal film which does nothave a light transmitting property, light can be transmitted through thefirst electrode layer 185 by forming the first electrode layer 185 verythin (preferably, a thickness of approximately 5 nm to 30 nm) so as tobe able to transmit light. A metal thin film which can be used for thefirst electrode layer 185 is a conductive film made of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof.

The first electrode layer 185 can be formed by an evaporation method, asputtering method, a CVD method, a printing method, a dispenser method,a droplet discharge method, or the like. In this embodiment mode, thefirst electrode layer 185 is manufactured by a sputtering method usingindium zinc oxide containing tungsten oxide. The first electrode layer185 preferably has a thickness in total of 100 nm to 800 nm.

The first electrode layer 185 may be polished by a CMP method or bycleaning with a polyvinyl alcohol-based porous body so that a surface ofthe first electrode layer 185 is planarized. After polishing by a CMPmethod, ultraviolet irradiation, oxygen plasma treatment, or the likemay be performed to the surface of the first electrode layer 185.

After the first electrode layer 185 is formed, heat treatment may beperformed. Through this heat treatment, moisture included in the firstelectrode layer 185 is released. Therefore, degasification or the likeis not caused in the first electrode layer 185. Even when a lightemitting material which is easily deteriorated by moisture is formedover the first electrode layer, the light emitting material is notdeteriorated. Accordingly, a highly reliable display device can bemanufactured.

Next, an insulating layer 186 (also called a partition, a barrier, orthe like) is formed to cover an end portion of the first electrode layer185, and the source electrode layer or the drain electrode layer.

The insulating layer 186 can be formed using silicon oxide, siliconnitride, silicon oxynitride, silicon nitride oxide, or the like and mayhave a single-layer structure or a stacked structure of two layers,three layers, or the like. The insulating film 186 can alternatively beformed using a material selected from substances including an inorganicinsulating material, such as aluminum nitride, aluminum oxynitridehaving a higher content of oxygen than that of nitrogen, aluminumnitride oxide having a higher content of nitrogen than that of oxygen,aluminum oxide, diamond-like carbon (DLC), nitrogen-containing carbon,or polysilazane. Alternatively, a material containing siloxane may beused. Furthermore, an organic insulating material may be used; anorganic material may be either photosensitive or non-photosensitive; andpolyimide, acrylic, polyamide, polyimide amide, a resist,benzocyclobutene, or polysilazane can be used. Moreover, an oxazoleresin can be used, and for example, a photo-curing polybenzoxazole orthe like can be used.

The insulating layer 186 can be formed by a sputtering method, a PVD(Physical Vapor Deposition) method, a CVD (Chemical Vapor Deposition)method such as a low-pressure CVD (LPCVD) method or a plasma CVD method,a droplet discharge method by which a pattern can be formed selectively,a printing method by which a pattern can be transferred or drawn (amethod for forming a pattern such as screen printing or offsetprinting), a dispenser method, a coating method such as a spin coatingmethod, a dipping method, or the like.

The etching into a desired shape may be performed by either plasmaetching (dry etching) or wet etching; however, plasma etching issuitable for treating a large-sized substrate. As an etching gas, afluorine-based gas such as CF₄ or NF₃ or a chlorine-based gas such asCl₂ or BCl₃ is used, to which an inert gas such as He or Ar may beappropriately added. Alternatively, electric discharge machining may beperformed locally when the etching process is performed usingatmospheric pressure discharge, in which case a mask layer does not needto be formed over the entire surface of the substrate.

In the connection region 205 shown in FIG. 9A, a wiring layer formed ofthe same material and in the same step as the second electrode layer iselectrically connected to the wiring layer which is formed of the samematerial and in the same step as the gate electrode layer.

An electroluminescent layer 188 is formed over the first electrode layer185. Note that, although FIG. 9B shows only one pixel, respectiveelectroluminescent layers corresponding to colors of R (red), G (green),and B (blue) are separately formed in this embodiment mode.

Next, a second electrode layer 189 is formed using a conductive filmover the electroluminescent layer 188. For the second electrode layer189, Al, Ag, Li, Ca, an alloy or a compound thereof such as MgAg, MgIn,AlLi, or CaF₂, or calcium nitride may be used. Thus, a light emittingelement 190 including the first electrode layer 185, theelectroluminescent layer 188, and the second electrode layer 189 isformed (see FIG. 9B).

In the display device of this embodiment mode shown in FIGS. 9A and 9B,light emitted from the light emitting element 190 is transmitted throughthe first electrode layer 185 and extracted in a direction indicated byan arrow in FIG. 9B.

In this embodiment mode, an insulating layer may be provided as apassivation film (protective film) over the second electrode layer 189.It is effective to provide a passivation film to cover the secondelectrode layer 189 in this manner. The passivation film can be formedusing a single layer or a stacked layer of an insulating film includingsilicon nitride, silicon oxide, silicon oxynitride, silicon nitrideoxide, aluminum nitride, aluminum oxynitride, aluminum nitride oxidehaving a higher content of nitrogen than that of oxygen, aluminum oxide,diamond-like carbon (DLC), or nitrogen-containing carbon. Alternatively,the passivation film may be formed using a siloxane resin.

In this case, a film providing good coverage is preferably used as thepassivation film. A carbon film, especially, a DLC film is effective.The DLC film can be formed at a temperature in the range of roomtemperature to 100° C.; therefore, the DLC film can be easily formedover the electroluminescent layer 188 having a low heat resistance. TheDLC film can be formed by a plasma CVD method (typically, an RF plasmaCVD method, a microwave CVD method, an electron cyclotron resonance(ECR) CVD method, a thermal filament CVD method, or the like), acombustion flame method, a sputtering method, an ion beam evaporationmethod, a laser evaporation method, or the like. A hydrogen gas and ahydrocarbon-based gas (for example, CH₄, C₂H₂, C₆H₆, or the like) areused as a reaction gas which is used for forming a DLC film. Thereaction gas is ionized by glow discharge, and the ions are acceleratedto collide with a negatively self-biased cathode; accordingly, a DLCfilm is formed. A CN film may be formed using a C₂H₄ gas and an N₂ gasas a reaction gas. The DLC film has a high blocking effect on oxygen andcan suppress oxidation of the electroluminescent layer 188. Accordingly,the electroluminescent layer 188 can be prevented from oxidizing duringa subsequent sealing step.

The substrate 100 provided with the light emitting element 190 and asealing substrate 195 are fixed to each other with a sealant 192 to sealthe light emitting element (see FIGS. 9A and 9B). As the sealant 192, itis typically preferable to use a visible light curable resin, anultraviolet ray curable resin, or a heat curable resin. For example, abisphenol-A liquid resin, a bisphenol-A solid resin, abromine-containing epoxy resin, a bisphenol-F resin, a bisphenol-ADresin, a phenol resin, a cresol resin, a novolac resin, a cycloaliphaticepoxy resin, an Epi-Bis type (Epichlorohydrin-Bisphenol) epoxy resin, aglycidyl ester resin, a glycidyl amine resin, a heterocyclic epoxyresin, or a modified epoxy resin can be used. Note that a regionsurrounded by the sealant may be filled with a filler 193, or nitrogenmay be enclosed by sealing the region in a nitrogen atmosphere. Sincethe display device of this embodiment mode is of bottom emission type,the filler 193 does not need to have a light transmitting property.However, in a case of employing a structure in which light is extractedthrough the filler 193, the filler 193 needs to have a lighttransmitting property. Typically, a visible light curing, ultravioletcuring, or thermosetting epoxy resin may be used. Through the abovesteps, a display device having a display function with the use of alight emitting element of this embodiment mode is completed.Alternatively, the filler can be dropped in a liquid state andencapsulated in the display device. When a substance having ahygroscopic property such as a drying agent is used as the filler, ahigher water-absorbing effect can be obtained, and element deteriorationcan be prevented.

In order to prevent element deterioration due to moisture, a dryingagent is provided in an EL display panel. In this embodiment mode, thedrying agent is provided in a depression portion formed in the sealingsubstrate so as to surround the pixel region, so that it does notinterfere with a reduction in thickness. Further, since the drying agenthaving a water-absorbing function is formed in a large area by formingthe drying agent in a region corresponding to the gate wiring layer, ahigh water-absorbing effect can be obtained. In addition, since thedrying agent is also formed over the gate wiring layer which does notcontribute to light emission, a reduction in light extraction efficiencycan be prevented.

This embodiment mode describes the case where the light emitting elementis sealed with a glass substrate. Sealing treatment is treatment forprotecting the light emitting element from moisture. Therefore, any ofthe following method can be used: a method in which a light emittingelement is mechanically sealed with a cover material, a method in whicha light emitting element is sealed with a thermosetting resin or anultraviolet curable resin, and a method in which a light emittingelement is sealed with a thin film of metal oxide, metal nitride, or thelike having high barrier capability. As the cover material, glass,ceramics, plastic, or a metal can be used. However, when light isemitted to the cover material side, the cover material needs to have alight-transmitting property. The cover material is attached to thesubstrate over which the above-mentioned light emitting element isformed, with a sealant such as a thermosetting resin or an ultravioletcurable resin, and a sealed space is formed by curing the resin withheat treatment or ultraviolet light irradiation treatment. It is alsoeffective to provide a moisture absorbing material typified by bariumoxide in the sealed space. The moisture absorbing material may beprovided on the sealant or over a partition or a peripheral portion soas not to block light emitted from the light emitting element. Further,a space between the cover material and the substrate over which thelight emitting element is formed can also be filled with a thermosettingresin or an ultraviolet curable resin. In this case, it is effective toadd a moisture absorbing material typified by barium oxide in thethermosetting resin or the ultraviolet curable resin.

FIG. 12 shows an example in which the source electrode or the drainelectrode layer is connected to the first electrode layer through awiring layer so as to be electrically connected instead of beingdirectly in contact, in the display device of FIGS. 9A and 9Bmanufactured in this embodiment mode. In the display device shown inFIG. 12, the source electrode layer or the drain electrode layer of thethin film transistor which drives the light emitting element iselectrically connected to a first electrode layer 395 through a wiringlayer 199. Moreover, in FIG. 12, the first electrode layer 395 ispartially stacked over the wiring layer 199; however, the firstelectrode layer 395 may be formed first and then the wiring layer 199may be formed on the first electrode layer 395.

In this embodiment mode, an FPC 194 is connected to the terminalelectrode layer 178 by an anisotropic conductive layer 196 in theexternal terminal connection region 202 so as to have an electricalconnection with outside. Moreover, as shown in FIG. 9A that is a topview of the display device, the display device manufactured in thisembodiment mode includes a peripheral driver circuit region 207 and aperipheral driver circuit region 208 having scan line driver circuits,in addition to the peripheral driver circuit region 204 and a peripheraldriver circuit region 209 having signal line driver circuits.

In this embodiment mode, the above-described circuits are used; however,the present invention is not limited thereto and an IC chip may bemounted as a peripheral driver circuit by a COG method or a TAB method.Moreover, a gate line driver circuit and a source line driver circuitmay be provided in any number.

In the display device of the present invention, a driving method forimage display is not particularly limited, and for example, a dotsequential driving method, a line sequential driving method, an areasequential driving method, or the like may be used. Typically, the linesequential driving method is used, and a time division gray scaledriving method or an area gray scale driving method may be appropriatelyused. Further, a video signal inputted to the source line of the displaydevice may be either an analog signal or a digital signal. The drivercircuit and the like may be appropriately designed in accordance withthe video signal.

Since each of the display devices shown in FIGS. 9A and 9B and FIG. 12has a bottom-emission structure, light is emitted through the substrate100. Therefore, a viewer side is on the substrate 100 side. Thus, alight-transmitting substrate is used as the substrate 100, and ananti-reflection film 177 is provided on an outer side that correspondsto a viewer side. The anti-reflection film 177 has a plurality ofprojections on its surface, and each projection has a conical shape inthis embodiment mode.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a rounded top,or the like. The anti-reflection film can be formed of not a materialwith a uniform refractive index but a material of which a refractiveindex changes from a surface to a display screen side. For example, ineach of the plurality of projections, a portion closer to the surface isformed of a material having a refractive index equivalent to air tofurther reduce reflection, by the projection surface, of external lightwhich is incident on each projection through air. On the other hand, aportion closer to the substrate on the display screen side is formed ofa material having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate. When a glass substrate is used as thesubstrate, since the refractive index of air is smaller than that of aglass substrate, each projection may have such a structure in which aportion closer to a surface (an apical portion in a case of a cone) isformed of a material having a lower refractive index, and a portioncloser to a base of each projection is formed of a material having ahigher refractive index, so that the refractive index increases from theapical portion to the base of the cone.

The display device including the anti-reflection film of the presentinvention includes a plurality of projections on its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 6

A display device having a light emitting element can be formed byapplying the present invention, and the emitting element emits light byany one of bottom emission, top emission, and dual emission. Thisembodiment mode describes examples of dual emission and top emissionwith reference to FIGS. 10 and 11.

A display device shown in FIG. 11 includes an element substrate 1600, athin film transistor 1655, a thin film transistor 1665, a thin filmtransistor 1675, a thin film transistor 1685, a first electrode layer1617, an electroluminescent layer 1619, a second electrode layer 1620, afiller 1622, a sealant 1632, an insulating film 1601 a, an insulatingfilm 1601 b, a gate insulating layer 1610, an insulating film 1611, aninsulating film 1612, an insulating layer 1614, a sealing substrate1625, a wiring layer 1633, a terminal electrode layer 1681, ananisotropic conductive layer 1682, an FPC 1683, and anti-reflectionfilms 1627 a and 1627 b. The display device also includes an externalterminal connection region 232, a sealing region 233, a peripheraldriver circuit region 234, and a pixel region 236. The filler 1622 canbe formed by a dropping method using a composition in a liquid state. Alight emitting display device is sealed by attaching the elementsubstrate 1600 provided with the filler by a dropping method and thesealing substrate 1625 to each other.

The display device shown in FIG. 11 has a dual-emission structure, inwhich light is emitted through both the element substrate 1600 and thesealing substrate 1625 in directions of arrows. Therefore, alight-transmitting electrode layer is used as each of the firstelectrode layer 1617 and the second electrode layer 1620.

In this embodiment mode, the first electrode layer 1617 and the secondelectrode layer 1620 each of which is a light-transmitting electrodelayer may be formed using a transparent conductive film made of aconductive material having a light-transmitting property, specifically,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. It is needless to say thatindium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide towhich silicon oxide is added (ITSO), or the like can also be used.

Even in a case of using a material such as a metal film which does nothave a light transmitting property, light can be transmitted through thefirst electrode layer 1617 and the second electrode layer 1620 byforming the first electrode layer 1617 and the second electrode layer1620 very thin (preferably, a thickness of approximately 5 nm to 30 nm)so as to be able to transmit light. A metal thin film which can be usedfor the first electrode layer 1617 and the second electrode layer 1620is a conductive film made of titanium, tungsten, nickel, gold, platinum,silver, aluminum, magnesium, calcium, lithium, or an alloy thereof.

As described above, the display device of FIG. 11 has a structure inwhich light emitted from a light emitting element 1605 is emitted fromboth sides through both the first electrode layer 1617 and the secondelectrode layer 1620.

A display device of FIG. 10 has a structure for top emission in adirection of an arrow. The display device shown in FIG. 10 includes anelement substrate 1300, a thin film transistor 1355, a thin filmtransistor 1365, a thin film transistor 1375, a thin film transistor1385, a wiring layer 1324, a first electrode layer 1317, anelectroluminescent layer 1319, a second electrode layer 1320, aprotective film 1321, a filler 1322, a sealant 1332, an insulating film1301 a, an insulating film 1301 b, a gate insulating layer 1310, aninsulating film 1311, an insulating film 1312, an insulating layer 1314,a sealing substrate 1325, a wiring layer 1333, a terminal electrodelayer 1381, an anisotropic conductive layer 1382, and an FPC 1383.

In each of the display devices in FIGS. 10 and 11, an insulating layerstacked over the terminal electrode layer is removed by etching. Whenthe display device has a structure in which an insulating layer havingmoisture permeability is not provided in the vicinity of a terminalelectrode layer, reliability is improved. The display device of FIG. 10includes an external terminal connection region 232, a sealing region233, a peripheral driver circuit region 234, and a pixel region 236. Inthe display device of FIG. 10, the wiring layer 1324 that is a metallayer having reflectivity is formed below the first electrode layer 1317in the display device having a dual emission structure shown in FIG. 11.The first electrode layer 1317 that is a transparent conductive film isformed over the wiring layer 1324. Since it is acceptable as long as thewiring layer 1324 has reflectivity, the wiring layer 1324 may be formedusing a conductive film made of titanium, tungsten, nickel, gold,platinum, silver, copper, tantalum, molybdenum, aluminum, magnesium,calcium, lithium, or an alloy thereof. It is preferable to use asubstance having reflectivity in a visible light range, and a TiN filmis used in this embodiment mode. In addition, the first electrode layer1317 may be formed using a conductive film, and in that case, the wiringlayer 1324 having reflectivity may be omitted.

Each of the first electrode layer 1317 and the second electrode layer1320 may be formed using a transparent conductive film made of aconductive material having a light-transmitting property, specifically,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. It is needless to say thatindium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide towhich silicon oxide is added (ITSO), or the like can also be used.

Even in a case of using a material such as a metal film which does nothave a light transmitting property, light can be transmitted through thesecond electrode layer 1320 by forming the second electrode layer 1320very thin (preferably, a thickness of approximately 5 nm to 30 nm) so asto be able to transmit light. A metal thin film which can be used as thesecond electrode layer 1320 is a conductive film made of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof.

Each pixel of the display device formed using the light emitting elementcan be driven by a simple matrix mode or an active matrix mode.Furthermore, either a digital drive or an analog drive may be employed.

A sealing substrate may be provided with a color filter (colored layer).The color filter (colored layer) can be formed by an evaporation methodor a droplet discharge method. When the color filter (colored layer) isused, high-definition display can also be performed. This is becausebroad peaks of emission spectra of R, G, and B can be corrected to sharppeaks by the color filter (colored layer).

Full color display can be achieved by using a material exhibitingmonochromatic light emission in combination with a color filter or acolor conversion layer. For example, the color filter (colored layer) orthe color conversion layer may be formed over the sealing substrate andthen attached to the element substrate.

Naturally, display with monochromatic light emission may be performed.For instance, an area-color display device using monochromatic lightemission may be formed. A passive-matrix display portion is suitable forthe area-color display device, and characters and symbols can be mainlydisplayed thereon.

Since the display device shown in FIG. 11 has a dual-emission structure,light is emitted through both the element substrate 1600 and the sealingsubstrate 1625. Therefore, a viewer side is on each of the elementsubstrate 1600 side and the sealing substrate 1625 side. Thus, alight-transmitting substrate is used as each of the element substrate1600 and the sealing substrate 1625, and the anti-reflection films 1627a and 1627 b are provided on respective outer sides that correspond toviewer sides. On the other hand, since the display device shown in FIG.10 has a top-emission structure, the sealing substrate 1325 on a viewerside is a light-transmitting substrate. An anti-reflection film 1327 isprovided on an outer side thereof. Each of the anti-reflection films1627 a, 1627 b, and 1327 has a plurality of projections on its surface,and each projection has a conical shape in this embodiment mode.

Instead of a conical shape, each projection may have a needle-likeshape, a shape of a cone with its apex cut off by a plane parallel toits base (a truncated conical shape), a dome shape with a rounded top,or the like. The anti-reflection film can be formed of not a materialwith a uniform refractive index but a material of which a refractiveindex changes from a surface to a display screen side. For example, ineach of the plurality of projections, a portion closer to the surface isformed of a material having a refractive index equivalent to air tofurther reduce reflection, by the projection surface, of external lightwhich is incident on each projection through air. On the other hand, aportion closer to the substrate on the display screen side is formed ofa material having a refractive index equivalent to that of the substrateto reduce reflection, by an interface between each projection and thesubstrate, of external light which propagates inside each projection andis incident on the substrate. When a glass substrate is used as thesubstrate, since the refractive index of air is smaller than that of aglass substrate, each projection may have such a structure in which aportion closer to a surface (an apical portion in a case of a cone) isformed of a material having a lower refractive index, and a portioncloser to a base of each projection is formed of a material having ahigher refractive index, so that the refractive index increases from theapical portion to the base of the cone.

The display device including the anti-reflection film of the presentinvention includes a plurality of projections over its surface. Externallight is reflected to not a viewer side but another adjacent projectionbecause an interface of each projection is not flat. Alternatively,external light propagates between the projections. Incident externallight is partly transmitted through each projection, and reflected lightis then incident on an adjacent projection. In this manner, externallight reflected by interfaces of adjacent projections repeats incidencebetween the projections.

In other words, the number of times of incidence of external lightentering the display device on the anti-reflection film is increased;therefore, the amount of external light transmitted through theanti-reflection film is increased. Thus, the amount of external lightreflected to a viewer side is reduced, and the cause of a reduction invisibility such as reflection can be eliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 7

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Specifically,this embodiment mode describes a light emitting display device using alight emitting element as a display element.

This embodiment mode describes a structure of a light emitting elementwhich can be employed as a display element of the display device of thepresent invention, with reference to FIGS. 22A to 22D.

FIGS. 22A to 22D each show an element structure of a light emittingelement. In the light emitting element, an electroluminescent layer 860,in which an organic compound and an inorganic compound are mixed, isinterposed between a first electrode layer 870 and a second electrodelayer 850. The electroluminescent layer 860 includes a first layer 804,a second layer 803, and a third layer 802 as shown, and in particular,the first layer 804 and the third layer 802 are highly characteristic.

The first layer 804 is a layer which functions to transport holes to thesecond layer 803, and includes at least a first organic compound and afirst inorganic compound showing an electron-accepting property to thefirst organic compound. What is important is that the first organiccompound and the first inorganic compound are not only simply mixed, butthe first inorganic compound shows an electron-accepting property to thefirst organic compound. This structure generates many holes (carriers)in the first organic compound, which originally has almost no inherentcarriers, and thus, a highly excellent hole-injecting property and ahighly excellent hole-transporting property can be obtained.

Therefore, the first layer 804 can have not only an advantageous effectthat is considered to be obtained by mixing an inorganic compound (suchas improvement in heat resistance) but also excellent conductivity(particularly a hole-injecting property and a hole-transporting propertyin the first layer 804). This excellent conductivity is an advantageouseffect that cannot be obtained in a conventional hole-transporting layerin which an organic compound and an inorganic compound, which do notelectronically interact with each other, are simply mixed. Thisadvantageous effect can make a drive voltage lower than a conventionalone. In addition, since the first layer 804 can be made thicker withoutcausing an increase in drive voltage, short circuit of the element dueto dust and the like can be suppressed.

It is preferable to use a hole-transporting organic compound as thefirst organic compound because holes (carriers) are generated in thefirst organic compound as described above. Examples of thehole-transporting organic compound include, but are not limited to,phthalocyanine (abbr.: H₂Pc), copper phthalocyanine (abbr.: CuPc),vanadyl phthalocyanine (abbr.: VOPc),4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbr.: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbr.:MTDATA), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene (abbr.: m-MTDAB),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(abbr.: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbr.:NPB), 4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl(abbr.: DNTPD), 4,4′,4″-tris(N-carbazolyl)triphenylamine (abbr.: TCTA),and the like. In addition, among the compounds mentioned above, aromaticamine compounds as typified by TDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD,and TCTA can easily generate holes (carriers), and are a suitable groupof compounds for the first organic compound.

On the other hand, the first inorganic compound may be any material aslong as the material can easily accept electrons from the first organiccompound, and various kinds of metal oxides and metal nitrides can beused. An oxide of a transition metal that belongs to any of Groups 4 to12 of the periodic table is preferable because such an oxide of atransition metal easily shows an electron-accepting property.Specifically, titanium oxide, zirconium oxide, vanadium oxide,molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide, zincoxide, or the like can be used. In addition, among the metal oxidesmentioned above, oxides of transition metals that belong to any ofGroups 4 to 8 have a higher electron-accepting property, which are apreferable group of compounds. In particular, vanadium oxide, molybdenumoxide, tungsten oxide, and rhenium oxide are preferable since they canbe formed by vacuum evaporation and can be easily handled.

Note that the first layer 804 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound.

Next, the third layer 802 is described. The third layer 802 is a layerwhich functions to transport electrons to the second layer 803, andincludes at least a third organic compound and a third inorganiccompound showing an electron-donating property to the third organiccompound. What is important is that the third organic compound and thethird inorganic compound are not only simply mixed but also the thirdinorganic compound shows an electron-donating property to the thirdorganic compound. This, structure generates many electrons (carriers) inthe third organic compound which has originally almost no inherentcarriers, and a highly excellent electron-injecting property and ahighly excellent electron-transporting property can be obtained.

Therefore, the third layer 802 can have not only an advantageous effectthat is considered to be obtained by mixing an inorganic compound (suchas improvement in heat resistance) but also excellent conductivity(particularly an electron-injecting property and anelectron-transporting property in the third layer 802). This excellentconductivity is an advantageous effect that cannot be obtained in aconventional electron-transporting layer in which an organic compoundand an inorganic compound, which do not electronically interact witheach other, are simply mixed. This advantageous effect can make a drivevoltage lower than the conventional one. In addition, since the thirdlayer 802 can be made thick without causing an increase in drivevoltage, short circuit of the element due to dust and the like can besuppressed.

It is preferable to use an electron-transporting organic compound as thethird organic compound because electrons (carriers) are generated in thethird organic compound as described above. Examples of theelectron-transporting organic compound include, but are not limited to,tris(8-quinolinolato)aluminum (abbr.: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbr.: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbr.: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbr.: BAlq),bis[2-(2′-hydroxyphenyl)benzoxazolato]zinc (abbr.: Zn(BOX)₂),bis[2-(2′-hydroxyphenyl)benzothiazolato]zinc (abbr.: Zn(BTZ)₂),bathophenanthroline (abbr.: BPhen), bathocuproin (abbr.: BCP),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbr.: PBD),1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbr.:OXD-7), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbr.: TPBI),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbr.:TAZ),3-(4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbr.: p-EtTAZ), and the like. In addition, among the compoundsmentioned above, chelate metal complexes each having a chelate ligandincluding an aromatic ring as typified by Alq₃, Almq₃, BeBq₂, BAlq,Zn(BOX)₂, Zn(BTZ)₂, and the like; organic compounds each having aphenanthroline skeleton as typified by BPhen, BCP, and the like; andorganic compounds having an oxadiazole skeleton as typified by PBD,OXD-7, and the like can easily generate electrons (carriers), and aresuitable groups of compounds for the third organic compound.

On the other hand, the third inorganic compound may be any material aslong as the material can easily donate electrons to the third organiccompound, and various kinds of metal oxide and metal nitride can beused. Alkali metal oxide, alkaline earth metal oxide, rare earth metaloxide, alkali metal nitride, alkaline earth metal nitride, and rareearth metal nitride are preferable because they easily show anelectron-donating property. Specifically, lithium oxide, strontiumoxide, barium oxide, erbium oxide, lithium nitride, magnesium nitride,calcium nitride, yttrium nitride, lanthanum nitride, and the like can beused. In particular, lithium oxide, barium oxide, lithium nitride,magnesium nitride, and calcium nitride are preferable because they canbe formed by vacuum evaporation and can be easily handled.

Note that the third layer 802 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound.

Next, the second layer 803 is described. The second layer 803 is a layerwhich functions to emit light, and includes a second organic compoundthat has a light emitting property. A second inorganic compound may alsobe included. The second layer 803 can be formed by using variouslight-emitting organic compounds and inorganic compounds. However, sinceit is believed to be hard to make a current flow through the secondlayer 803 as compared with the first layer 804 or the third layer 802,the thickness of the second layer 803 is preferably approximately 10 nmto 100 nm.

The second organic compound is not particularly limited as long as it isa light-emitting organic compound, and examples of the second organiccompound include, for example, 9,10-di(2-naphthyl)anthracene (abbr.:DNA), 9,10-di(2-naphthyl)-2-tert-butylanthracene (abbr.: t-BuDNA),4,4′-bis(2,2-diphenylvinyl)biphenyl (abbr.: DPVBi), coumarin 30,coumarin 6, coumarin 545, coumarin 545T, perylene, rubrene,periflanthene, 2,5,8,11-tetra(tert-butyl)perylene (abbr.: TBP),9,10-diphenylanthracene (abbr.: DPA), 5,12-diphenyltetracene,4-(dicyanomethylene)-2-methyl-[p-(dimethylamino)styryl]-4H-pyran (abbr.:DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)ethenyl]-4H-pyran(abbr.: DCM2),4-(dicyanomethylene)-2,6-bis[p-(dimethylamino)styryl]-4H-pyran (abbr.:BisDCM), and the like. In addition, it is also possible to use acompound capable of generating phosphorescence such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(picolinate)(abbr.: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(picolinate)(abbr.: Ir(CF₃ppy)₂(pic)), tris(2-phenylpyridinato-N,C^(2′))iridium(abbr.: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(acetylacetonate) (abbr.:Ir(PPY)₂(acac)),bis[2-(2′-thienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate) (abbr.:Ir(thp)₂(acac)),bis(2-phenylquinolinato-N,C^(2′))iridium(acetylacetonate) (abbr.:Ir(pq)₂(acac)), orbis[2-(2′-benzothienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate)(abbr.: Ir(btp)₂(acac)).

A triplet excitation light-emitting material containing a metal complexor the like may be used for the second layer 803 in addition to asinglet excitation light-emitting material. For example, among pixelsemitting red, green, and blue light, the pixel emitting red light whoseluminance is reduced by half in a relatively short time is formed byusing a triplet excitation light-emitting material and the other pixelsare formed by using a singlet excitation light-emitting material. Atriplet excitation light-emitting material has a feature of favorablelight-emitting efficiency and less power consumption to obtain the sameluminance. In other words, when a triplet excitation light-emittingmaterial is used for a red pixel, only a small amount of current needsto be applied to a light-emitting element, and thus, reliability can beimproved. A pixel emitting red light and a pixel emitting green lightmay be formed using a triplet excitation light-emitting material and apixel emitting blue light may be formed using a singlet excitationlight-emitting material to reduce power consumption. Power consumptioncan be further reduced by forming a light-emitting element which emitsgreen light that is highly visible to human eyes by using a tripletexcitation light-emitting material.

The second layer 803 may include not only the second organic compound asdescribed above, which produces light emission, but also another organiccompound. Examples of organic compounds that can be added include, butare not limited to, TDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD, TCTA, Alq₃,Almq₃, BeBq₂, BAlq, Zn(BOX)₂, Zn(BTZ)₂, BPhen, BCP, PBD, OXD-7, TPBI,TAZ, p-EtTAZ, DNA, t-BUDNA, and DPVBi, which are mentioned above, andfurther, 4,4′-bis(N-carbazolyl)biphenyl (abbr.: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbr.: TCPB), and the like.It is preferable that the organic compound, which is added in additionto the second organic compound, have higher excitation energy than thatof the second organic compound and be added in larger amounts than thesecond organic compound in order to make the second organic compoundemit light efficiently (which makes it possible to prevent concentrationquenching of the second organic compound). Alternatively, as anotherfunction, the added organic compound may emit light along with thesecond organic compound (which makes it possible to emit white light orthe like).

The second layer 803 may have a structure in which light emitting layershaving different light emission wavelength bands are each formed inpixels so as to perform color display. Typically, light emitting layerscorresponding to respective luminescent colors of R (red), G (green),and B (blue) are formed. In this case, color purity can be improved andspecular surface (reflection) of a pixel portion can be prevented byproviding a filter that transmits light of a certain light emissionwavelength band on a light emission side of the pixels. By providing thefilter, a circular polarizing plate or the like, which has beenconventionally thought to be required, can be omitted, thereby reducingloss of light emitted from the light emitting layers. In addition, achange in hue, which is caused in the case where a pixel portion (adisplay screen) is seen obliquely, can be reduced.

The material which can be used for the second layer 803 is preferableeither a low-molecular organic light-emitting material or a highmolecular organic light emitting material. A high molecular organiclight emitting material has high physical strength in comparison with alow molecular material, and a durability of an element is high. Inaddition, manufacturing of an element is relatively easy because a highmolecular organic light emitting material can be formed by coating.

Since the color of light is determined by a material of the lightemitting layer, a light emitting element that emits light of a desiredcolor can be formed by selecting the material. As the high molecularelectroluminescent material that can be used to form the light emittinglayer, a polyparaphenylene vinylene based material, a polyparaphenylenebased material, a polythiophene based material, or a polyfluorene basedmaterial can be given.

As the polyparaphenylene vinylene based material, a derivative ofpoly(paraphenylenevinylene) [PPV]:poly(2,5-dialkoxy-1,4-phenylenevinylene) [RO-PPV];poly[2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene] [MEH-PPV];poly[2-(dialkoxyphenyl)-1,4-phenylenevinylene] [ROPh-PPV]; or the likecan be used. As the polyparaphenylene based material, a derivative ofpolyparaphenylene [PPP]: poly(2,5-dialkoxy-1,4-phenylene) [RO-PPP];poly(2,5-dihexoxy-1,4-phenylene); or the like can be used. As thepolythiophene based material, a derivative of polythiophene [PT]:poly(3-alkylthiophene) [PAT]; poly(3-hexylthiophene) [PHT];poly(3-cyclohexylthiophene) [PCHT]; poly(3-cyclohexyl-4-methylthiophene)[PCHMT]; poly(3,4-dicyclohexylthiophene) [PDCHT];poly[3-(4-octylphenyl)-thiophene] [POPT];poly[3-(4-octylphenyl)-2,2-bithiophene] [PTOPT]; or the like can beused. As the polyfluorene based material, a derivative of polyfluorene[PF]: poly(9,9-dialkylfluorene) [PDAF]; poly(9,9-dioctylfluorene)[PDOF]; or the like can be given.

The second inorganic compound may be any inorganic compound as long asthe inorganic compound does not easily quench light emission of thesecond organic compound, and various kinds of metal oxide and metalnitride can be used. In particular, an oxide of a metal that belongs toGroup 13 or 14 of the periodic table is preferable because lightemission of the second organic compound is not easily quenched by suchan oxide, and specifically, aluminum oxide, gallium oxide, siliconoxide, and germanium oxide are preferable. However, the second inorganiccompound is not limited thereto.

Note that the second layer 803 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound. A layer structure of thelight-emitting layer can be changed, and an electrode layer forinjecting electrons may be provided or a light-emitting material may bedispersed, instead of providing a specific electron-injecting region orlight-emitting region. Such a change can be permitted unless it departsfrom the spirit of the present invention.

A light emitting element formed using the above-described material emitslight when biased forwardly. A pixel of a display device formed with thelight emitting element can be driven by a simple matrix mode or anactive matrix mode. In either mode, each pixel is made to emit light byapplying a forward bias thereto in specific timing, and the pixel is ina non-light-emitting state for a certain period. By applying a reversebias at this non-light-emitting time, reliability of the light emittingelement can be improved. In the light emitting element, there is adeterioration mode in which emission intensity is decreased underspecific driving conditions or a deterioration mode in which anon-light-emitting region is enlarged in the pixel and luminance isapparently decreased. However, progression of deterioration can beslowed down by alternating driving. Thus, reliability of the lightemitting display device can be improved. Either a digital drive or ananalog drive can be employed.

Thus, a color filter (colored layer) may be formed over a sealingsubstrate. The color filter (colored layer) can be formed by anevaporation method or a droplet discharge method. When the color filter(colored layer) is used, high-definition display can also be performed.This is because broad peaks of the emission spectra of R, G, and B canbe corrected to sharp peaks by the color filter (colored layer).

Full color display can be achieved by forming a material exhibitingmonochromatic light emission in combination with a color filter or acolor conversion layer. For example, the color filter (colored layer) orthe color conversion layer may be formed over the sealing substrate andthen attached to the element substrate.

Naturally, display with monochromatic light emission may be performed.For instance, an area-color display device using monochromatic lightemission may be formed. A passive-matrix display portion is suitable forthe area-color display device, and characters and symbols can be mainlydisplayed thereon.

Materials of the first electrode layer 870 and the second electrodelayer 850 need to be selected considering the work function. The firstelectrode layer 870 and the second electrode layer 850 can be either ananode or a cathode depending on the pixel structure. In the case wherepolarity of a driving thin film transistor is a p-channel type, thefirst electrode layer 870 may serve as an anode and the second electrodelayer 850 may serve as a cathode as shown in FIG. 22A. In the case wherepolarity of the driving thin film transistor is an n-channel type, thefirst electrode layer 870 may serve as a cathode and the secondelectrode layer 850 may serve as an anode as shown in FIG. 22B.Materials that can be used for the first electrode layer 870 and thesecond electrode layer 850 is described. It is preferable to use amaterial having a higher work function (specifically, a material havinga work function of 4.5 eV or higher) for one of the first electrodelayer 870 and the second electrode layer 850, which serves as an anode,and a material having a lower work function (specifically, a materialhaving a work function of 3.5 eV or lower) for the other electrode layerwhich serves as a cathode. However, since the first layer 804 issuperior in a hole-injecting property and a hole-transporting propertyand the third layer 802 is superior in an electron-injecting propertyand an electron transporting property, both of the first electrode layer870 and the second electrode layer 850 are scarcely restricted by a workfunction, and various materials can be used.

Each of the light-emitting elements shown in FIGS. 22A and 22B has astructure in which light is extracted through the first electrode layer870, and thus, the second electrode layer 850 does not necessarily needto have a light-transmitting property. The second electrode layer 850may be formed of a film mainly including an element selected from Ti,Ni, W, Cr, Pt, Zn, Sn, In, Ta, Al, Cu, Au, Ag, Mg, Ca, Li, or Mo, or analloy material or compound material containing the element as its maincomponent such as TiN, TiSi_(X)N_(Y), WSi_(X), WN_(X), WSi_(X)N_(Y), NbNor a stacked film thereof with a total thickness ranging from 100 nm to800 nm.

The second electrode layer 850 can be formed by an evaporation method, asputtering method, a CVD method, a printing method, a dispenser method,a droplet discharge method, or the like.

In addition, when the second electrode layer 850 is formed using alight-transmitting conductive material, like the material used for thefirst electrode layer 870, light is also extracted through the secondelectrode layer 850, and a dual emission structure can be obtained, inwhich light emitted from the light-emitting element is emitted to bothof the first electrode layer 870 side and the second electrode layer 850side.

Note that the light emitting element according to the present inventionhas many variations by changing types of the first electrode layer 870and the second electrode layer 850.

FIG. 22B shows a case where the third layer 802, the second layer 803,and the first layer 804 are provided in this order from the firstelectrode layer 870 side in the electroluminescent layer 860.

As described above, in the light-emitting element of the presentinvention, a layer interposed between the first electrode layer 870 andthe second electrode layer 850 is formed from the electroluminescentlayer 860 including a layer in which an organic compound and aninorganic compound are combined. The light emitting element is anorganic-inorganic composite light-emitting element provided with layers(that is, the first layer 804 and the third layer 802) that providefunctions such as a high carrier-injecting property and acarrier-transporting property by mixing an organic compound and aninorganic compound, where the functions are not obtainable with eitherthe organic compound or the inorganic compound. Further, the first layer804 and the third layer 802 need to be layers in which an organiccompound and an inorganic compound are combined, particularly whenprovided on the first electrode layer 870 side, and may contain only oneof an organic compound and an inorganic compound when provided on thesecond electrode layer 850 side.

Further, various methods can be used as a method for forming theelectroluminescent layer 860, which is a layer in which an organiccompound and an inorganic compound are mixed. For example, the methodsinclude a co-evaporation method of evaporating both an organic compoundand an inorganic compound by resistance heating. In addition, forco-evaporation, an inorganic compound may be evaporated by an electronbeam (EB) while evaporating an organic compound by resistance heating.Further, the methods also include a method of sputtering an inorganiccompound while evaporating an organic compound by resistance heating todeposit the both at the same time. In addition, the electroluminescentlayer may also be formed by a wet process.

Similarly, the first electrode layer 870 and the second electrode layer850 can be formed by evaporation by resistance heating, EB evaporation,sputtering, a wet process, and the like.

In FIG. 22C, an electrode layer having reflectivity is used for thefirst electrode layer 870, and an electrode layer having alight-transmitting property is used for the second electrode layer 850in the structure of FIG. 22A. Light emitted from the light-emittingelement is reflected by the first electrode layer 870, then, transmittedthrough the second electrode layer 850, and is emitted to outside.Similarly, in FIG. 22D, an electrode layer having reflectivity is usedfor the first electrode layer 870, and an electrode layer having alight-transmitting property is used for the second electrode layer 850in the structure of FIG. 22B. Light emitted from the light-emittingelement is reflected by the first electrode layer 870, then, transmittedthrough the second electrode layer 850, and is emitted to outside.

This embodiment mode can be freely combined with the above-describedembodiment mode regarding the display device including the lightemitting element.

In the display device of this embodiment mode, an anti-reflection filmhaving a plurality of projections is also provided over a display screensurface of the display device. Accordingly, the number of times ofincidence of external light entering the display device on theanti-reflection film is increased; therefore, the amount of externallight transmitted through the anti-reflection film is increased. Thus,the amount of external light reflected to a viewer side is reduced, andthe cause of a reduction in visibility such as reflection can beeliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 3, 5, and 6 as appropriate.

Embodiment Mode 8

This embodiment mode describes an example of a display device having ananti-reflection function that can further reduce reflection of externallight, for the purpose of providing excellent visibility. Specifically,this embodiment mode describes a light emitting display device using alight emitting element as a display element. This embodiment modedescribes a structure of a light emitting element which can be appliedas a display element of the display device of the present invention,with reference to FIGS. 23A to 24C.

Light emitting elements utilizing electroluminescence are classifiedaccording to whether a light emitting material is an organic compound oran inorganic compound. In general, the former is referred to as anorganic EL element, and the latter is referred to as an inorganic ELelement.

The inorganic EL elements are classified according to their elementstructures into a dispersed inorganic EL element and a thin-filminorganic EL element. They are different in that the former includes anelectroluminescent layer in which particles of a light emitting materialare dispersed in a binder and the latter includes an electroluminescentlayer formed of a thin film of a light emitting material; however, theyare common in that they require electrons accelerated by a high electricfield. Note that a mechanism for obtainable light emission includes adonor-acceptor recombination light emission which utilizes a donor leveland an acceptor level and a localized light emission which utilizesinner-shell electron transition of metal ions. In general, it is oftenthe case that the dispersed inorganic EL element performs thedonor-acceptor recombination light emission and the thin-film inorganicEL element performs the localized light emission.

A light emitting material which can be used in the present inventionincludes a base material and an impurity element serving as a lightemitting center. Light emission of various colors can be obtained bychanging impurity elements to be contained. As a method for producing alight emitting material, various methods such as a solid phase methodand a liquid phase method (coprecipitation method) can be used. Inaddition, a liquid phase method such as a spray pyrolysis method, adouble decomposition method, a method by precursor pyrolysis, a reversemicelle method, a combined method of one of these methods andhigh-temperature baking, or a freeze-drying method can be used.

The solid phase method is a method by which a base material and animpurity element or a compound containing an impurity element areweighed, mixed in a mortar, and reacted by heating and baking in anelectric furnace to make the impurity element contained in the basematerial. The baking temperature is preferably in the range of 700° C.to 1500° C. This is because solid phase reaction does not proceed whenthe temperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form. The methodrequires baking at a relatively high temperature; however, it is asimple method. Therefore, the method provides good productivity and issuitable for mass production.

The liquid phase method (coprecipitation method) is a method by which abase material or a compound containing a base material is reacted in asolution with an impurity element or a compound containing an impurityelement and the reactant is baked after being dried. Particles of thelight emitting material are uniformly distributed, a particle size issmall, and the reaction proceeds even at a low baking temperature.

As the base material used for a light emitting material, sulfide, oxide,or nitride can be used. As sulfide, zinc sulfide (ZnS), cadmium sulfide(CdS), calcium sulfide (CaS), yttrium sulfide (Y₂S₃), gallium sulfide(Ga₂S₃), strontium sulfide (SrS), barium sulfide (BaS), or the like canbe used, for example. As oxide, zinc oxide (ZnO), yttrium oxide (Y₂O₃),or the like can be used, for example. As nitride, aluminum nitride(AlN), gallium nitride (GaN), indium nitride (InN), or the like can beused, for example. Further, zinc selenide (ZnSe), zinc telluride (ZnTe),or the like can also be used. It may be a ternary mixed crystal such ascalcium gallium sulfide (CaGa₂S₄), strontium gallium sulfide (SrGa₂S₄),or barium gallium sulfide (BaGa₂S₄).

As the light emitting center of localized light emission, manganese(Mn), copper (Cu), samarium (Sm), terbium (Tb), erbium (Er), thulium(Tm), europium (Eu), cerium (Ce), praseodymium (Pr), or the like can beused. Note that a halogen element such as fluorine (F) or chlorine (Cl)may be added. A halogen element can also function as a chargecompensation.

On the other hand, as the light emitting center of donor-acceptorrecombination light emission, a light emitting material which contains afirst impurity element forming a donor level and a second impurityelement forming an acceptor level can be used. As the first impurityelement, fluorine (F), chlorine (Cl), aluminum (Al), or the like can beused, for example. As the second impurity element, copper (Cu), silver(Ag), or the like can be used, for example.

In a case of synthesizing the light emitting material of donor-acceptorrecombination light emission by a solid phase method, a base material, afirst impurity element or a compound containing a first impurityelement, and a second impurity element or a compound containing a secondimpurity element are separately weighed, mixed in a mortar, and thenheated and baked in an electric furnace. As the base material, theabove-mentioned base material can be used. As the first impurity elementor the compound containing the first impurity element, fluorine (F),chlorine (Cl), aluminum sulfate (Al₂S₃), or the like can be used, forexample. As the second impurity element or the compound containing thesecond impurity element, copper (Cu), silver (Ag), copper sulfide(Cu₂S), silver sulfide (Ag₂S), or the like can be used, for example. Thebaking temperature is preferably in the range of 700° C. to 1500° C.This is because solid phase reaction does not proceed when thetemperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form.

As the impurity element in the case of utilizing solid phase reaction, acompound including the first impurity element and the second impurityelement may be used. In this case, the impurity element is easilydiffused and the solid phase reaction easily proceeds, so that a uniformlight emitting material can be obtained. Furthermore, a high-puritylight emitting material can be obtained because an unnecessary impurityelement is not mixed. As the compound including the first impurityelement and the second impurity element, copper chloride (CuCl), silverchloride (AgCl), or the like can be used, for example.

Note that the concentration of the impurity element to the base materialmay be in the range of 0.01 atomic % to 10 atomic %, preferably 0.05atomic % to 5 atomic %.

In the case of the thin-film inorganic EL element, theelectroluminescent layer is a layer containing the above-described lightemitting material, which can be formed by a vacuum evaporation methodsuch as a resistance heating evaporation method or an electron beamevaporation (EB evaporation) method, a physical vapor deposition (PVD)method such as a sputtering method, a chemical vapor deposition (CVD)method such as a metal organic CVD method or a low-pressure hydridetransport CVD method, an atomic layer epitaxy (ALE) method, or the like.

FIGS. 23A to 23C show examples of a thin-film inorganic EL element whichcan be used as a light emitting element. In each of FIGS. 23A to 23C, alight emitting element includes a first electrode layer 50, anelectroluminescent layer 51, and a second electrode layer 53.

Each of the light emitting elements shown in FIGS. 23B and 23C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light emitting element inFIG. 23A. The light emitting element shown in FIG. 23B includes aninsulating layer 54 between the first electrode layer 50 and theelectroluminescent layer 52. The light emitting element shown in FIG.23C includes an insulating layer 54 a between the first electrode layer50 and the electroluminescent layer 52 and an insulating layer 54 bbetween the second electrode layer 53 and the electroluminescent layer52. As described above, the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodelayers sandwiching the electroluminescent layer. The insulating layermay be a single layer or a stack of a plurality of layers.

In FIG. 23B, the insulating layer 54 is provided in contact with thefirst electrode layer 50. However, the insulating layer 54 may beprovided in contact with the second electrode layer 53 by reversing theorder of the insulating layer and the electroluminescent layer.

In the case of the dispersed inorganic EL element, a particulate lightemitting material is dispersed in a binder to form a film-likeelectroluminescent layer. In a case where a particle having a desiredsize cannot be sufficiently obtained by a production method of a lightemitting material, the material may be processed into particles bycrushing in a mortar or the like. The binder is a substance for fixing aparticulate light emitting material in a dispersed manner and holdingthe material in shape as the electroluminescent layer. The lightemitting material is uniformly dispersed and fixed in theelectroluminescent layer by the binder.

In the case of the dispersed inorganic EL element, theelectroluminescent layer can be formed by a droplet discharge methodwhich can selectively form the electroluminescent layer, a printingmethod (such as screen printing or off-set printing), a coating methodsuch as a spin-coating method, a dipping method, a dispenser method, orthe like. The thickness is not particularly limited, but it ispreferably in the range of 10 nm to 1000 nm. In addition, in theelectroluminescent layer containing the light emitting material and thebinder, the proportion of the light emitting material is preferably inthe range of 50 wt % to 80 wt %.

FIGS. 24A to 24C show examples of a dispersed inorganic EL element whichcan be used as a light emitting element. A light emitting element inFIG. 24A has a stacked structure of a first electrode layer 60, anelectroluminescent layer 62, and a second electrode layer 63, andcontains a light emitting material 61 held by a binder in theelectroluminescent layer 62.

As the binder which can be used in this embodiment mode, an organicmaterial, an inorganic material, or a mixed material of an organicmaterial and an inorganic material can be used. As an organic material,a polymer having a relatively high dielectric constant, such as acyanoethyl cellulose resin, or a resin such as polyethylene,polypropylene, a polystyrene resin, a silicone resin, an epoxy resin, orvinylidene fluoride can be used. Alternatively, a heat resistant highmolecular compound such as aromatic polyamide or polybenzimidazole, or asiloxane resin may be used. Note that the siloxane resin corresponds toa resin including a Si—O—Si bond. Siloxane includes a skeleton formedfrom a bond of silicon (Si) and oxygen (O). An organic group containingat least hydrogen (for example, an alkyl group or aromatic hydrocarbon)or a fluoro group may be used for a substituent, or an organic groupcontaining at least hydrogen and a fluoro group may be used forsubstituents. Alternatively, a resin material such as a vinyl resin likepolyvinyl alcohol or polyvinylbutyral, a phenol resin, a novolac resin,an acrylic resin, a melamine resin, a urethane resin, or an oxazoleresin (polybenzoxazole) may be used. A dielectric constant can beadjusted by appropriately mixing high dielectric constant fine particlesof barium titanate (BaTiO₃), strontium titanate (SrTiO₃), or the like inthe above resin.

As an inorganic material included in the binder, a material selectedfrom substances containing inorganic materials can be used, such assilicon oxide (SiO_(X)), silicon nitride (SiN_(X)), silicon containingoxygen and nitrogen, aluminum nitride (AlN), aluminum containing oxygenand nitrogen, aluminum oxide (Al₂O₃), titanium oxide (TiO₂), BaTiO₃,SrTiO₃, lead titanate (PbTiO₃), potassium niobate (KNbO₃), lead niobate(PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalate (BaTa₂O₆), lithiumtantalate (LiTaO₃), yttrium oxide (Y₂O₃), or zirconium oxide (ZrO₂). Adielectric constant of the electroluminescent layer including the lightemitting material and the binder can be controlled by making an organicmaterial contain a high dielectric constant inorganic material (byaddition or the like), so that a dielectric constant can be increased.When a mixed layer of an inorganic material and an organic material isused as a binder to obtain high dielectric constant, a higher electriccharge can be induced in the light emitting material.

In a producing process, a light emitting material is dispersed in asolution including a binder. As a solvent of the solution including thebinder that can be used in this embodiment mode, a solvent in which abinder material is soluble and which can produce a solution having aviscosity suitable for a method for forming the electroluminescent layer(various wet processes) and a desired thickness, may be selectedappropriately. An organic solvent or the like can be used. In the caseof using, for example, a siloxane resin as the binder, propylene glycolmonomethyl ether, propylene glycol monomethyl ether acetate (alsoreferred to as PGMEA), 3-methoxy-3-methyl-1-butanol (also referred to asMMB), or the like can be used.

Each of the light emitting elements shown in FIGS. 24B and 24C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light emitting element inFIG. 24A. The light emitting element shown in FIG. 24B includes aninsulating layer 64 between the first electrode layer 60 and theelectroluminescent layer 62. The light emitting element shown in FIG.24C includes an insulating layer 64 a between the first electrode layer60 and the electroluminescent layer 62 and an insulating layer 64 bbetween the second electrode layer 63 and the electroluminescent layer62. As described above, the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodessandwiching the electroluminescent layer. In addition, the insulatinglayer may be a single layer or a stack of a plurality of layers.

In FIG. 24B, the insulating layer 64 is provided in contact with thefirst electrode layer 60. However, the insulating layer 64 may beprovided in contact with the second electrode layer 63 by reversing theorder of the insulating layer and the electroluminescent layer.

An insulating layer such as the insulating layer 54 in FIGS. 23A to 23Cor the insulating layer 64 in FIGS. 24A to 24C is not particularlylimited, but it preferably has high withstand voltage and dense filmquality. Furthermore, it preferably has a high dielectric constant. Forexample, a film of silicon oxide (SiO₂), yttrium oxide (Y₂O₃), titaniumoxide (TiO₂), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), tantalumoxide (Ta₂O₅), barium titanate (BaTiO₃), strontium titanate (SrTiO₃),lead titanate (PbTiO₃), silicon nitride (Si₃N₄), zirconium oxide (ZrO₂),or the like, a mixed film thereof, or a stacked film of two or morekinds can be used. These insulating films can be formed by sputtering,evaporation, CVD, or the like. Alternatively, the insulating layer maybe formed by dispersing particles of the insulating material in abinder. A binder material may be formed using a material and a methodsimilar to those of the binder included in the electroluminescent layer.The thickness is not particularly limited, but it is preferably in therange of 10 nm to 1000 nm.

The light emitting element described in this embodiment mode, which canprovide light emission by applying voltage between a pair of electrodelayers sandwiching the electroluminescent layer, can be operated byeither DC drive or AC drive.

In the display device of this embodiment mode, an anti-reflection filmhaving a plurality of projections is also provided over a display screensurface of the display device. Accordingly, the number of times ofincidence of external light entering the display device on theanti-reflection film is increased; therefore, the amount of externallight transmitted through the anti-reflection film is increased. Thus,the amount of external light reflected to a viewer side is reduced, andthe cause of a reduction in visibility such as reflection can beeliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 3, 5, and 6 as appropriate.

Embodiment Mode 9

This embodiment mode describes a structure of a backlight. A backlightis provided in a display device as a backlight unit having a lightsource. In the backlight unit, the light source is surrounded by areflector plate so that light is scattered efficiently.

As shown in FIG. 16A, a cold cathode tube 401 can be used as a lightsource in a backlight unit 352. In order to efficiently reflect light bythe cold cathode tube 401, a lamp reflector 332 can be provided. Thecold cathode tube 401 is mostly used for a large-sized display devicedue to the intensity of the luminance from the cold cathode tube.Therefore, the backlight unit having a cold cathode tube can be used fora display of a personal computer.

As shown in FIG. 16B, a light emitting diode (LED) 402 can be used as alight source in the backlight unit 352. For example, light emittingdiodes (W) 402 emitting light of a white color are arranged atpredetermined intervals. In order to efficiently reflect light by thelight emitting diode (W) 402, the lamp reflector 332 can be provided.

As shown in FIG. 16C, light emitting diodes (LED) 403, 404, and 405emitting light of colors of RGB can be used as a light source in thebacklight unit 352. When the light emitting diodes (LED) 403, 404, and405 emitting light of colors of RGB are used, color reproducibility canbe enhanced as compared with a case when only the light emitting diode(W) 402 emitting light of a white color is used. In order to efficientlyreflect light by the light emission diodes, the lamp reflector 332 canbe provided.

As shown in FIG. 16D, when light emitting diodes (LED) 403, 404, and 405emitting light of colors of RGB is used as a light source, it is notnecessary that the number and arrangement thereof are the same for all.For example, a plurality of light emitting diodes emitting light of acolor that has low light emitting intensity (such as green) may bearranged.

Furthermore, the light emitting diode 402 emitting light of a whitecolor and the light emitting diodes (LED) 403, 404, and 405 emittinglight of colors of RGB may be combined.

When a field sequential mode is applied in a case of using the lightemitting diodes of RGB, color display can be performed by sequentiallylighting the light emitting diodes of RGB in accordance with the time.

The light emitting diode is suitable for a large-sized display devicebecause the luminance thereof is high. In addition, colorreproducibility of the light emitting diode is superior to that of acold cathode tube because the color purity of each color of RGB isfavorable, and an area required for arrangement can be reduced.Therefore, a narrower frame can be achieved when the light emittingdiode is applied to a small-sized display device.

Further, a light source does not need to be provided as the backlightunits shown in FIGS. 16A to 16D. For example, when a backlight having alight emitting diode is mounted on a large-sized display device, thelight emitting diode can be arranged on the back side of the substrate.In this case, each of the light emitting diodes can be sequentiallyarranged at predetermined intervals. Color reproducibility can beenhanced in accordance with the arrangement of the light emittingdiodes.

By providing a display device using such a backlight with ananti-reflection film having a plurality of projections on its surface,the display device can have a high anti-reflection function that canfurther reduce reflection of external light and can have highvisibility. Accordingly, a more high-quality and high-performancedisplay device can be manufactured. A backlight having a light emittingdiode is particularly suitable for a large-sized display device, and ahigh-quality image can be provided even in a dark place by enhancing thecontrast ratio of the large-sized display device.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 4 as appropriate.

Embodiment Mode 10

FIG. 15 shows an example of forming an EL display module manufactured byapplying the present invention. In FIG. 15, a pixel portion includingpixels is formed over a substrate 2800. A flexible substrate is used aseach of the substrate 2800 and a sealing substrate 2820.

In FIG. 15, a TFT which has a similar structure to that formed in thepixel, or a protective circuit portion 2801 operated in a similar mannerto a diode by connecting a gate to either a source or a drain of the TFTis provided between a driver circuit and the pixel and outside the pixelportion. A driver IC formed of a single crystalline semiconductor, astick driver IC formed of a polycrystalline semiconductor film over aglass substrate, a driver circuit formed of a SAS, or the like isapplied to a driver circuit 2809.

The substrate 2800 to which an element layer is transferred is fixed tothe sealing substrate 2820 with spacers 2806 a and 2806 b formed by adroplet discharge method interposed therebetween. The spacers arepreferably provided to keep a distance between two substrates constanteven when the substrate is thin or an area of the pixel portion isenlarged. A space between the substrate 2800 and the sealing substrate2820 over light emitting elements 2804 and 2805 connected to TFTs 2802and 2803 respectively may be filled with a light-transmitting resinmaterial and the resin material may be solidified, or may be filled withanhydrous nitrogen or an inert gas. An anti-reflection film 2827 withprojections is provided on an outer side of the sealing substrate 2820which corresponds to a viewer side.

FIG. 15 shows a case where the light emitting elements 2804 and 2805have a top-emission structure, in which light is emitted in thedirection of arrows shown in the drawing. Multicolor display can beperformed by making the pixels emit light of different colors of red,green, and blue. At this time, color purity of the light emitted outsidecan be improved by forming colored layers 2807 a to 2807 c correspondingto respective colors on the sealing substrate 2820 side. Moreover,pixels which emit white light may be used and may be combined with thecolored layers 2807 a to 2807 c.

The driver circuit 2809 which is an external circuit is connected by awiring board 2810 to a scan line or signal line connection terminalwhich is provided at one end of an external circuit substrate 2811. Inaddition, a heat pipe 2813, which is a high-efficiency heat conductiondevice having a pipe-like shape, and a heat sink 2812 may be provided incontact with or adjacent to the substrate 2800 to enhance a heatdissipation effect.

Note that FIG. 15 shows the top-emission EL module; however, a bottomemission structure may be employed by changing the structure of thelight emitting element or the disposition of the external circuit board.Naturally, a dual emission structure in which light is emitted from boththe top and bottom surfaces may be used. In the case of the top emissionstructure, the insulating layer serving as a partition may be coloredand used as a black matrix. This partition can be formed by a dropletdischarge method and it may be formed by mixing a black resin of apigment material, carbon black, or the like into a resin material suchas polyimide. A stack thereof may alternatively be used.

In addition, reflected light of light which is incident from outside maybe blocked by using a retardation plate or a polarizing plate. Aninsulating layer serving as a partition may be colored and used as ablack matrix. This partition can be formed by a droplet dischargemethod. Carbon black or the like may be mixed into a resin material suchas polyimide, and a stack thereof may also be used. By a dropletdischarge method, different materials may be discharged to the sameregion plural times to form the partition. A quarter-wave plate or ahalf-wave plate may be used as the retardation plate and may be designedto be able to control light. As the structure, a TFT element substrate,the light emitting element, the sealing substrate (sealant), theretardation plate (quarter-wave plate or a half-wave plate), and thepolarizing plate are sequentially stacked, through which light emittedfrom the light emitting element is transmitted and emitted outside fromthe polarizing plate side. The retardation plate or polarizing plate maybe provided on a side where light is emitted or may be provided on bothsides in the case of a dual emission display device in which light isemitted from the both surfaces. In addition, an anti-reflection film maybe provided on the outer side of the polarizing plate. Accordingly, amore high-definition and accurate image can be displayed.

In this embodiment mode, the anti-reflection film having a plurality ofprojections is provided over a substrate on a viewer side. In a sealingstructure on a side opposite to the viewer side with respect to theelement, a sealing structure may be formed by attaching a resin film tothe side where the pixel portion is formed, with the use of a sealant oran adhesive resin. Various sealing methods such as resin sealing using aresin, plastic sealing using plastic, and film sealing using a film canbe used. A gas barrier film which prevents water vapor from penetratingthe resin film is preferably provided over the surface of the resinfilm. By employing a film sealing structure, further reductions inthickness and weight can be achieved.

In the display device of this embodiment mode, an anti-reflection filmhaving a plurality of projections is also provided over a display screensurface of the display device. Accordingly, the number of times ofincidence of external light entering the display device on theanti-reflection film is increased; therefore, the amount of externallight transmitted through the anti-reflection film is increased. Thus,the amount of external light reflected to a viewer side is reduced, andthe cause of a reduction in visibility such as reflection can beeliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by providing the anti-reflection filmhaving a plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 3, and 5 to 8 as appropriate.

Embodiment Mode 11

This embodiment mode is described with reference to FIGS. 14A and 14B.FIGS. 14A and 14B show examples of forming a display device (liquidcrystal display module) by using a TFT substrate 2600 manufactured inaccordance with the present invention.

FIG. 14A shows an example of a liquid crystal display module, in whichthe TFT substrate 2600 and an opposite substrate 2601 are fixed to eachother with a sealant 2602, and a pixel portion 2603 including a TFT, adisplay element 2604 including a liquid crystal layer, a colored layer2605, and a polarizing plate 2606 are provided between the substrates toform a display region. The colored layer 2605 is necessary to performcolor display. In the case of the RGB system, respective colored layerscorresponding to colors of red, green, and blue are provided forrespective pixels. The outer sides of the TFT substrate 2600 and theopposite substrate 2601 are provided with an anti-reflection film 2626,the polarizing plate 2607, and a diffuser plate 2613, and the polarizingplate 2606 is provided between the TFT substrate 2600 and the oppositesubstrate 2601. A light source includes a cold cathode tube 2610 and areflector plate 2611. A circuit board 2612 is connected to the TFTsubstrate 2600 by a flexible wiring board 2609. External circuits suchas a control circuit and a power supply circuit are incorporated in thecircuit board 2612. The polarizing plate and the liquid crystal layermay be stacked with a retardation plate interposed therebetween.

The display device in FIG. 14A is an example in which theanti-reflection film 2626 is provided on an outer side of the oppositesubstrate 2601, and the polarizing plate 2606 and the colored layer 2605are sequentially provided on an inner side. However, the polarizingplate 2606 may be provided on the outer side of the opposite substrate2601 (on a viewer side), and in that case, the anti-reflection film 2626may be provided over a surface of the polarizing plate 2606. The stackedstructure of the polarizing plate 2606 and the colored layer 2605 isalso not limited to that shown in FIG. 14A and may be appropriately setdepending on materials of the polarizing plate 2606 and the coloredlayer 2605 or conditions of manufacturing steps.

The liquid crystal display module can employ a TN (Twisted Nematic)mode, an IPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching)mode, an MVA (Multi-domain Vertical Alignment) mode, a PVA (PatternedVertical Alignment) mode, an ASM (Axially Symmetric aligned Micro-cell)mode, an OCB (Optical Compensated Birefringence) mode, an FLC(Ferroelectric Liquid Crystal) mode, an AFLC (Anti Ferroelectric LiquidCrystal) mode, or the like.

FIG. 14B shows an example of applying an OCB mode to the liquid crystaldisplay module of FIG. 14A, so that this liquid crystal display moduleis an FS-LCD (Field Sequential-LCD). The FS-LCD performs red, green, andblue light emissions in one frame period. Color display can be performedby composing an image by a time division method. Also, emission of eachcolor is performed using a light emitting diode, a cold cathode tube, orthe like; hence, a color filter is not required. There is no necessityfor arranging color filters of three primary colors and limiting adisplay region of each color. Display of all three colors can beperformed in any region. On the other hand, light emission of threecolors is performed in one frame period; therefore, high speed responseof liquid crystal is needed. When an FLC mode using an FS system and theOCB mode are applied to the display device of the present invention, adisplay device or a liquid crystal television device having higherperformance and high image quality can be completed.

A liquid crystal layer of the OCB mode has, what is called, a π cellstructure. In the π cell structure, liquid crystal molecules areoriented such that pretilt angles of the molecules are symmetrical withrespect to the center plane between the active matrix substrate and theopposite substrate. The orientation in the π cell structure is a splayorientation when a voltage is not applied between the substrates, andshifts into a bend orientation when the voltage is applied. Whitedisplay is performed in this bend orientation. Further voltageapplication makes the liquid crystal molecules in the bend orientationorientated perpendicular to the substrates, which does not allow lightto pass therethrough. Note that a response speed approximately ten timesas high as that of a conventional TN mode can be achieved by using theOCB mode.

Further, as a mode corresponding to the FS system, an HV(Half V)-FLC, anSS(Surface Stabilized)-FLC, or the like using a ferroelectric liquidcrystal (FLC) that can be operated at high speed can also be used. Anematic liquid crystal that has relatively low viscosity can be used forthe OCB mode. A smectic liquid crystal that has a ferroelectric phasecan be used for the HV-FLC or the SS-FLC.

An optical response speed of the liquid crystal display module isincreased by narrowing a cell gap of the liquid crystal display module.Alternatively, the optical response speed can be increased by loweringthe viscosity of the liquid crystal material. The above method ofincreasing the optical response speed is more effective when a pixelpitch of a pixel region of a TN-mode liquid crystal display module is 30μm or less. The optical response speed can be further increased by anoverdrive method in which an applied voltage is increased (or decreased)only for a moment.

The liquid crystal display module of FIG. 14B is a transmissive liquidcrystal display module, in which a red light source 2910 a, a greenlight source 2910 b, and a blue light source 2910 c are provided aslight sources. A control portion 2912 is provided in the liquid crystaldisplay module to separately control the red light source 2910 a, thegreen light source 2910 b, and the blue light source 2910 c to be turnedon or off. The light emission of each color is controlled by the controlportion 2912, and light enters the liquid crystal to compose an imageusing the time division, thereby performing color display.

In the display device of this embodiment mode, an anti-reflection filmhaving a plurality of projections is also provided over a display screensurface of the display device. Accordingly, the number of times ofincidence of external light entering the display device on theanti-reflection film is increased; therefore, the amount of externallight transmitted through the anti-reflection film is increased. Thus,the amount of external light reflected to a viewer side is reduced, andthe cause of a reduction in visibility such as reflection can beeliminated.

The present invention can provide a high-visibility display devicehaving a high anti-reflection function that can further reducereflection of external light by including an anti-reflection film havinga plurality of projections on its surface. Accordingly, a morehigh-quality and high-performance display device can be manufactured.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 4, and 9 as appropriate.

Embodiment Mode 12

With the display device formed by the present invention, a televisiondevice (also referred to as simply a television, or a televisionreceiver) can be completed. FIG. 19 is a block diagram showing maincomponents of the television device.

FIG. 17A is a top view showing a structure of a display panel accordingto the present invention. A pixel portion 2701 in which pixels 2702 arearranged in matrix, a scan line input terminal 2703, and a signal lineinput terminal 2704 are formed over a substrate 2700 having aninsulating surface. The number of pixels may be determined in accordancewith various standards. In a case of XGA full-color display using RGB,the number of pixels may be 1024×768×3 (RGB). In a case of UXGAfull-color display using RGB, the number of pixels may be 1600×1200×3(RGB), and in a case of full-spec, high-definition, and full-colordisplay using RGB, the number may be 1920×1080×3 (RGB).

The pixels 2702 are formed in matrix by intersections of scan linesextended from the scan line input terminal 2703 and signal linesextended from the signal line input terminal 2704. Each pixel 2702 inthe pixel portion 2701 is provided with a switching element and a pixelelectrode layer connected thereto. A typical example of the switchingelement is a TFT. A gate electrode layer of the TFT is connected to thescan line, and a source or a drain of the TFT is connected to the signalline, which enables each pixel to be independently controlled by asignal inputted from the outside.

FIG. 17A shows a structure of a display panel in which a signal to beinputted to the scan line and the signal line is controlled by anexternal driver circuit. Alternatively, a driver IC 2751 may be mountedon the substrate 2700 by a COG (Chip On Glass) method as shown in FIG.18A. As another mounting mode, a TAB (Tape Automated Bonding) method maybe used as shown in FIG. 18B. The driver IC may be formed over a singlecrystalline semiconductor substrate or may be formed using a TFT over aglass substrate. In each of FIGS. 18A and 18B, the driver IC 2751 isconnected to an FPC (Flexible Printed Circuit) 2750.

When a TFT provided in a pixel is formed of a crystalline semiconductor,a scan line driver circuit 3702 can be formed over a substrate 3700 asshown in FIG. 17B. In FIG. 17B, a pixel portion 3701 is controlled by anexternal driver circuit connected to a signal line input terminal 3704,similarly to FIG. 17A. When the TFT provided in a pixel is formed of apolycrystalline (microcrystalline) semiconductor, a single crystallinesemiconductor, or the like having high mobility, a pixel portion 4701, ascan line driver circuit 4702, and a signal line driver circuit 4704 canall be formed over a glass substrate 4700 as shown in FIG. 17C.

As for the display panel, there are the following cases: a case in whichonly a pixel portion 901 is formed as shown in FIG. 17A and a scan linedriver circuit 903 and a signal line driver circuit 902 are mounted by aTAB method as shown in FIG. 18B; a case in which the scan line drivercircuit 903 and the signal line driver circuit 902 are mounted by a COGmethod as shown in FIG. 18A; a case in which a TFT is formed as shown inFIG. 17B, the pixel portion 901 and the scan line driver circuit 903 areformed over a substrate, and the signal line driver circuit 902 isseparately mounted as a driver IC; a case in which the pixel portion901, the signal line driver circuit 902, and the scan line drivercircuit 903 are formed over a substrate as shown in FIG. 17C; and thelike. The display panel may have any of the structures.

As another external circuit in FIG. 19, a video signal amplifier circuit905 which amplifies a video signal among signals received by a tuner904, a video signal processing circuit 906 which converts the signalsoutputted from the video signal amplifier circuit 905 into chrominancesignals corresponding to respective colors of red, green, and blue, acontrol circuit 907 which converts the video signal into an inputspecification of the driver IC, and the like are provided on an inputside of the video signal. The control circuit 907 outputs signals toboth a scan line side and a signal line side. In the case of digitaldrive, a signal dividing circuit 908 may be provided on the signal lineside and an input digital signal may be divided into m pieces andsupplied.

An audio signal among signals received by the tuner 904 is sent to anaudio signal amplifier circuit 909 and is supplied to a speaker 913through an audio signal processing circuit 910. A control circuit 911receives control information of a receiving station (receptionfrequency) or sound volume from an input portion 912 and transmitssignals to the tuner 904 and the audio signal processing circuit 910.

A television device can be completed by incorporating the display moduleinto a chassis as shown in FIGS. 20A and 20B. When a liquid crystaldisplay module is used as a display module, a liquid crystal televisiondevice can be manufactured. When an EL display module is used, an ELtelevision device can be manufactured. Alternatively, a plasmatelevision, electronic paper, or the like can be manufactured. In FIG.20A, a main screen 2003 is formed by using the display module, and aspeaker portion 2009, an operation switch, and the like are provided asits accessory equipment. Thus, a television device can be completed inaccordance with the present invention.

A display panel 2002 is incorporated in a chassis 2001, and general TVbroadcast can be received by a receiver 2005. When the display device isconnected to a communication network by wired or wireless connectionsvia a modem 2004, one-way (from a sender to a receiver) or two-way(between a sender and a receiver or between receivers) informationcommunication can be performed. The television device can be operated byusing a switch built in the chassis 2001 or a remote control unit 2006.A display portion 2007 for displaying output information may also beprovided in the remote control device 2006.

Further, the television device may include a sub screen 2008 formedusing a second display panel so as to display channels, volume, or thelike, in addition to the main screen 2003. In this structure, both themain screen 2003 and the sub screen 2008 can be formed using the liquidcrystal display panel of the present invention. Alternatively, the mainscreen 2003 may be formed using an EL display panel having a wideviewing angle, and the sub screen 2008 may be formed using a liquidcrystal display panel capable of displaying images with less powerconsumption. In order to reduce the power consumption preferentially,the main screen 2003 may be formed using a liquid crystal display panel,and the sub screen may be formed using an EL display panel, which can beswitched on and off. In accordance with the present invention, ahigh-reliability display device can be formed even when a large-sizedsubstrate is used and a large number of TFTs or electronic componentsare used.

FIG. 20B shows a television device having a large-sized display portion,for example, a 20-inch to 80-inch display portion. The television deviceincludes a chassis 2010, a display portion 2011, a remote control device2012 that is an operation portion, a speaker portion 2013, and the like.The present invention is applied to manufacturing of the display portion2011. Since the television device in FIG. 20B is a wall-hanging type, itdoes not require a large installation space.

Naturally, the present invention is not limited to the televisiondevice, and can be applied to various use applications as a large-sizeddisplay medium such as an information display board at a train station,an airport, or the like, or an advertisement display board on thestreet, as well as a monitor of a personal computer.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 11 as appropriate.

Embodiment Mode 13

Examples of electronic devices in accordance with the present inventionare as follows: a television device (also referred to as simply atelevision, or a television receiver), a camera such as a digital cameraor a digital video camera, a cellular telephone device (simply alsoreferred to as a cellular phone or a cell-phone), an informationterminal such as PDA, a portable game machine, a computer monitor, acomputer, a sound reproducing device such as a car audio system, animage reproducing device including a recording medium, such as ahome-use game machine, and the like. Preferred modes of them aredescribed with reference to FIGS. 21A to 21E.

A portable information terminal device shown in FIG. 21A includes a mainbody 9201, a display portion 9202, and the like. The display device ofthe present invention can be applied to the display portion 9202. As aresult, a high-performance portable information terminal device whichcan display a high-quality image with high visibility can be provided.

A digital video camera shown in FIG. 21B includes a display portion9701, a display portion 9702, and the like. The display device of thepresent invention can be applied to the display portion 9701. As aresult, a high-performance digital video camera which can display ahigh-quality image with high visibility can be provided.

A cellular phone shown in FIG. 21C includes a main body 9101, a displayportion 9102, and the like. The display device of the present inventioncan be applied to the display portion 9102. As a result, ahigh-performance cellular phone which can display a high-quality imagewith high visibility can be provided.

A portable television device shown in FIG. 21D includes a main body9301, a display portion 9302 and the like. The display device of thepresent invention can be applied to the display portion 9302. As aresult, a high-performance portable television device which can displaya high-quality image with high visibility can be provided. The displaydevice of the present invention can be applied to a wide range oftelevision devices ranging from a small-sized television device mountedon a portable terminal such as a cellular phone, a medium-sizedtelevision device which can be carried, to a large-sized (for example,40-inch or larger) television device.

A portable computer shown in FIG. 21E includes a main body 9401, adisplay portion 9402, and the like. The display device of the presentinvention can be applied to the display portion 9402. As a result, ahigh-performance portable computer which can display a high-qualityimage with high visibility can be provided.

As described above, a high-performance electronic device which candisplay a high-quality image with high visibility can be provided byusing the display device of the present invention.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 12.

Embodiment 1

This embodiment describes the result of optical calculation of theanti-reflection film used in the present invention. In addition, theoptical calculation of an anti-reflection film having a stackedstructure was also performed for comparison. In this embodiment, thedescription is given with reference to Tables 1 and 2 and FIGS. 26 to30.

The calculation in this embodiment was performed using an opticalcalculation simulator for optical devices, FullWAVE (manufactured byRSoft Design Group, Inc.). The reflectance was calculated by 2D opticalcalculation.

As a comparative example, the reflection of external light by ananti-reflection film with a multilayer structure which is formed by astack of a low refractive index layer and a high refractive index layerwas calculated. As the comparative example, an anti-reflection film 11including a high refractive index layer 11 a (n=1.9) and a lowrefractive index layer 11 b (n=1.34) is formed over a glass substrate 10(n=1.52, reflectance: 4%), and a surface of the low refractive indexlayer 11 b is exposed to air 12 (n=1.0) as shown in FIG. 26. Table 1shows the components, each reflectance, and each thickness of thecomparative example. TABLE 1 thickness component refractive index [μm]air 12 1 8 low refractive index layer 11b (Q: λ/4) 1.34 0.103 highrefractive index layer 11a (H: λ/2) 1.9 0.145 glass substrate 10 1.52 8

Note that the high refractive index layer 11 a is a thin film in whichan optical path length (actual distance×refractive index) is set to aquarter of a wavelength λ of 550 nm having high luminous efficacy (thethin film is also referred to as Q: quarter-wave film), and the lowrefractive index layer 11 b is a thin film in which an optical pathlength (actual distance×refractive index) is set to a half of awavelength of 550 nm having high luminous efficacy (the thin film isalso referred to as H: half-wave film). Therefore, the anti-reflectionfilm 11 is a so-called QH type anti-reflection film. Light thatcorresponds to external light is perpendicularly incident on the glasssubstrate 10 and the anti-reflection film 11 from above through air, andreflected light that is reflected by the glass substrate 10 and theanti-reflection film 11 to the air side was detected by a monitor 14.Light emitted from a light source 13 passes through an air layer and isincident on the low refractive index layer 11 b, the high refractiveindex layer 11 a, and the glass substrate 10.

FIG. 27 shows the relationship between a wavelength and a reflectance inthe comparative example. As shown in FIG. 27, the reflectance is notconstant in a measured wavelength range from 380 nm to 780 nm whichcorresponds to a visible light range, and wavelength dependence can beobserved. The reflectance is 1% or less at a wavelength of approximately450 nm to 750 nm, whereas the reflectance is increased in ashort-wavelength range of 450 nm or less and a long-wavelength range of750 nm or more. This increase in reflectance was particularly noticeableat a short wavelength of 450 nm or less, or ultraviolet light. In a caseof such a stacked structure as the comparative example, it is confirmedthat it is difficult to obtain constant low reflectance in a measuredwavelength range of 380 nm to 780 nm which corresponds to a visiblelight range and it is only possible to decrease the reflectance byapproximately 1% even in the vicinity of 550 nm.

The reflection of external light by the anti-reflection film havingprojections on its surface using the present invention was calculated.In this embodiment, a plurality of adjacent conical projections are usedas samples A1 to A8, and each projection is an isosceles triangle in across section perpendicular to the base, as shown in FIG. 28. In FIG.28, projections 21 are provided over a substrate 20. As shown in thecross-sectional view, an angle θ that is an angle of a slope isdetermined depending on a ratio of a cone height H to a base diameter L.The samples A1 to A8 respectively have ratios of cone heights H to basediameters L of 29:1, 10:1, 9.5:1, 5.7:1, 4.1:1, 2.8:1, 2.4:1, and 1.9:1and have angles θ of 89, 87.2, 87, 85, 83, 80, 78, and 75 (deg.).Reflectances of light corresponding to external light, which is incidenton the samples A1 to A8 and reflected by the anti-reflection films eachhaving projections, were calculated. Table 2 shows the angles θ, theheights H: the diameters (bases) L, the heights H, and the diameters(bases) L in cross-sections of the samples A1 to A8. TABLE 2 projectionstructure A1 A2 A3 A4 A5 A6 A7 A8 θ [deg] 89 87.2 87 85 83 80 78 75 H:L29:1 10:1 9.5:1 5.7:1 4.1:1 2.8:1 2.4:1 1.9:1 H [μm] 2.86 1.02 0.9540.572 0.407 0.284 0.235 0.187 L [μm] 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Each projection was made of silicon nitride containing oxygen. Arefractive index thereof was set relative to a wavelength of light (forexample, a refractive index, 1.48 (a wavelength, 380 nm), 1.47 (awavelength, 550 nm), or 1.46 (a wavelength, 780 nm). A substrateprovided with the anti-reflection film having projections was a glasssubstrate (with a refractive index of 1.52).

FIG. 29 shows the relationship between a wavelength of external lightand each reflectance of the samples A1 to A8. As shown in FIG. 29, eachreflectance of the samples A1 to A5 was approximately 0.2% or less in ameasured visible light wavelength range (380 nm to 700 nm), whereas eachreflectance of the samples A6 to A8 was approximately 0.2% or more inthe visible light wavelength range and was high, approximately 0.4% to0.8%, at certain wavelength. FIG. 30 is a graph showing the result ofFIG. 29 in the relationship between an angle of an oblique line of eachprojection and a mean reflectance at the measured wavelength. The sampleA1 has an angle of 89°; the sample A2, 87.2°; the sample A3, 87°; thesample A4, 85°; the sample A5, 83°; the sample A6, 80°; the sample A7,78°; and the sample A8, 75°. The mean reflectance is 0.1% or less at anangle of 84° or more and less than 90°, whereas the mean reflectance issharply increased at 82° and 80° up to approximately 0.25%. From thisresult, the reflection of external light can be reduced to 0.1% or lesswhen the angle of an oblique line of each projection is equal to orgreater than 84° and less than 90°. Thus, it is confirmed that theanti-reflection film of the present invention can exert a highanti-reflection effect.

Embodiment 2

In this embodiment, the reflection of external light by theanti-reflection film having projections on its surface using the presentinvention was calculated. This embodiment is described with reference toTable 3, and FIGS. 31 and 32.

The reflection of external light by the anti-reflection film havingprojections on its surface using the present invention was calculated.Also in this embodiment, a plurality of adjacent conical projections areused as samples B similarly to Embodiment 1, and each projection is anisosceles triangle in a cross section perpendicular to the base, asshown in FIG. 28. As shown in the cross-sectional view, an angle θ isdetermined depending on a ratio of a cone height H to a base diameter L.Samples B1 to B6 respectively have cone heights H of 1.0 μm, 1.5 μm, 2.0μm, 2.25 μm, 2.5 μm, and 3.0 μm and accordingly have base diameters L of0.1 μm, 0.15 μm, 0.20 μm, 0.225 μm, 0.25 μm, and 0.30 μm so that eachratio of the cone height H to the base diameter L is 10:1 and the angleθ is kept constant at 87.2 (deg.) where low reflectance is exhibited inFIG. 30. Reflectances of light corresponding to external light, which isincident on the samples B1 to B6 and reflected by the anti-reflectionfilms each having projections, were calculated. Table 3 shows the anglesθ, the heights H: the diameters (bases) L, the heights H, and thediameters (bases) L in cross-sections of the samples B1 to B6. TABLE 3projection structure B1 B2 B3 B4 B5 B6 θ [deg] 87.2 87.2 87.2 87.2 87.287.2 H:L 10:1 10:1 10:1 10:1 10:1 10:1 H [μm] 1.0 1.5 2 2.25 2.5 3 L[μm] 0.10 0.15 0.20 0.225 0.25 0.30

Each projection was made of silicon nitride containing oxygen. Arefractive index thereof was set relative to a wavelength of light (forexample, a refractive index, 1.48 (a wavelength, 380 nm), 1.47 (awavelength, 550 nm), or 1.46 (a wavelength, 780 nm). A substrateprovided with the anti-reflection film having projections was a glasssubstrate (with a refractive index of 1.52).

FIG. 31 shows the relationship between a wavelength of external lightand each reflectance of the samples B1 to B6. As shown in FIG. 31, eachreflectance of the samples B1 to B6 was approximately 0.08% or less in ameasured visible light wavelength range (380 nm to 700 nm). FIG. 32 is agraph showing the result of FIG. 31 in the relationship between a heightof each projection and a mean reflectance at the measured wavelength.The sample B1 has a height of 1 μm; the sample B2, 1.5 μm; the sampleB3, 2.0 μm; the sample B4, 2.25 μm; the sample B5, 2.5 μm; and thesample B6, 3 μm. The mean reflectance is 0.04% or less with the heightof 1 μm to 3 μm. From this result, it is confirmed that when the angleof an oblique line of each projection is at 87.2°, the reflectance ofexternal light can be reduced to 0.04% or less with the height in therange of 1 μm to 3 μm and a high anti-reflection effect can be exerted.In addition, when each projection has a height of 1 μm to 3 μm, visiblelight transmittance thereof is not decreased.

Embodiment 3

In this embodiment, the reflection of external light by theanti-reflection film having projections on its surface using the presentinvention was calculated. This embodiment is described with reference toTable 4 and FIGS. 33 to 35.

The reflection of external light by the anti-reflection film havingprojections on its surface using the present invention was calculated.In this embodiment, a plurality of adjacent conical projections eachwith an upper base surface are used as samples C1 to C7, and eachprojection is trapezoidal in a cross section perpendicular to the base,as shown in FIG. 33. In FIG. 33, projections 31 are provided over asubstrate (a glass substrate) 30. As shown in the cross-sectional view,a height of each trapezoid is 1 μm, and an angle θ is determineddepending on a ratio of an upper base diameter (referred to as an upperbase a) to a lower base diameter (referred to as a lower base b). Thesamples C1 to C7 respectively have ratios of upper bases a to lowerbases b of 0, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.2. Reflectances oflight corresponding to external light, which is incident on the samplesC1 to C7 and reflected by the anti-reflection films each havingprojections, were calculated. Note that the sample Cl having the ratioof the upper base a to the lower base b of 0 has a conical shape with noupper base surface. Table 4 shows the ratios of the upper bases a to thelower bases b in cross-sections of the samples C1 to C7. TABLE 4projection structure C1 C2 C3 C4 C5 C6 C7 a/b 0 0.05 0.075 0.1 0.1250.15 0.2

Each projection was made of silicon nitride containing oxygen. Arefractive index thereof was set relative to a wavelength of light (forexample, a refractive index, 1.48 (a wavelength, 380 nm), 1.47 (awavelength, 550 nm), or 1.46 (a wavelength, 780 nm). A substrateprovided with the anti-reflection film having projections was a glasssubstrate (with a refractive index of 1.52).

FIG. 34 shows the relationship between a wavelength of external lightand each reflectance of the samples C1 to C7. As shown in FIG. 34, eachreflectance of the samples C1 to C7 was approximately 0.35% or less in ameasured visible light wavelength range (380 nm to 700 nm). FIG. 35 is agraph showing the result of FIG. 34 in the relationship between theupper bases a/the lower bases b showing the ratios of the upper bases ato the lower bases b and a mean reflectance at the measured wavelength.The sample C1 has an upper base a/a lower base b of 0; the sample C2,0.05; the sample C3, 0.075; the sample C4, 0.1; the sample C5, 0.125;the sample C6, 0.15; and the sample C7, 0.2. Note that the meanreflectance is gradually increased as the ratio is increased. However,the mean reflectance is approximately 0.3% or less when the ratio is 0to 0.2. The reason is considered as follows: as the value of upper basea/lower base b is increased, the angle θ of an oblique line is increasedand further, the area of the upper base surface is also increased;therefore, reflection of external light by the upper base surface isincreased. From this result, it is confirmed that at a projectionincluding an upper base surface and a lower base surface, thereflectance of external light can be reduced to approximately 0.35% orless and the mean reflectance to approximately 0.3% or less when theratio of the upper base to the lower base is 0.2 or less, and that ahigh anti-reflection effect can be exerted.

This application is based on Japanese Patent Application serial no.2006-151921 filed in Japan Patent Office on May 31, 2006, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising an anti-reflection film, theanti-reflection film comprising a plurality of projections over adisplay screen, wherein an angle made by a base and a slope of each ofthe plurality of projections is equal to or greater than 84° and lessthan 90°.
 2. A display device comprising: a first substrate, a secondsubstrate being a light-transmitting substrate over the first substrate;a display element provided between the first and second substrates; andan anti-reflection film comprising a plurality of projections over thesecond substrate, wherein an angle made by a base and a slope of each ofthe plurality of projections is equal to or greater than 84° and lessthan 90°.
 3. A display device comprising: a first substrate being alight-transmitting substrate; a second substrate being alight-transmitting substrate over the first substrate; a display elementprovided between the first and second substrates; and a firstanti-reflection film under the first substrate, the firstanti-reflection film comprising a first plurality of projections, asecond anti-reflection film over the second substrate, the secondanti-reflection film comprising a second plurality of projections,wherein an angle made by a base and a slope of each of the first andsecond plurality of projections is equal to or greater than 84° and lessthan 90°.
 4. The display device according to claim 2, further comprisinga polarizing plate between the light-transmitting substrate and theanti-reflection film.
 5. The display device according to claim 1 orclaim 2, wherein each of the plurality of projections has a conicalshape.
 6. The display device according to claims 1 or claim 2, whereineach of the plurality of projections has a shape of a cone with a flator round apex.
 7. The display device according to claim 1 or claim 2,wherein each of the plurality of projections has a shape that a cone isstacked over a cylinder.
 8. The display device according to claim 1 orclaim 2, wherein a height of each of the plurality of projections ismore than five times and less than twenty-nine times a diameter of thebase.
 9. The display device according to claim 1 or claim 2, wherein theplurality of projections are adjacent to each other.
 10. The displaydevice according to claim 1, wherein a refractive index of each of theplurality of projections continuously changes toward the substrate. 11.The display device according to claim 2 or claim 3, wherein the displayelement is a liquid crystal element.
 12. The display device according toclaim 2 or claim 3, wherein the display element is a light emittingelement.
 13. The display device according to claim 1 or claim 2, whereineach of the plurality of projections has a height of 1 μm to 3 μm and abase diameter of 0.1 μm to 0.3 μm.
 14. An electronic device having thedisplay device according to any one of claims 1 to 3, wherein theelectronic device is selected from the group consisting of a televisiondevice, a portable information terminal device, a digital video camera,a cellular phone, a portable television device, and a portable computer.15. The display device according to claim 3, further comprising apolarizing plate between the second substrate and the secondanti-reflection film.
 16. The display device according to claim 3,wherein each of the second plurality of projections has a conical shape.17. The display device according to claim 3, wherein each of the secondplurality of projections has a shape of a cone with a flat or roundapex.
 18. The display device according to claim 3, wherein each of thesecond plurality of projections has a shape that a cone is stacked overa cylinder.
 19. The display device according to claim 3, wherein aheight of each of the second plurality of projections is more than fivetimes and less than twenty-nine times a diameter of the base.
 20. Thedisplay device according to claims 3, wherein the first plurality ofprojections are adjacent to each other, and the second plurality ofprojections are adjacent to each other.
 21. The display device accordingto claim 2, wherein a refractive index of each of the plurality ofprojections continuously changes toward the second substrate.
 22. Thedisplay device according to claim 3, wherein a refractive index of eachof the first plurality of projections continuously changes toward thefirst substrate, and a refractive index of each of the second pluralityof projections continuously changes toward the second substrate.
 23. Thedisplay device according to claim 1 or claim 2, wherein each of thefirst and second plurality of projections has a height of 1 μm to 3 μmand a base diameter of 0.1 μm to 0.3 μm.
 24. The display deviceaccording to claim 2 or claim 3, further comprising a polarizing platebetween the display element and the second substrate.